John Kendrew (1917-1997)

John Kendrew building a model of myoglobin. Credit: MRC Laboratory of Molecular Biology.

[Ed Note: Today we remember Sir John Kendrew, who would have turned one-hundred years old on March 24th.]

The Cavendish Laboratory at Cambridge University was an exciting place to be in the 1950s. While James Watson and Francis Crick worked themselves into a frenzy in their race with Linus Pauling to discover the structure of DNA, lab-mate John Kendrew worked quietly alongside another future Nobel laureate, Max Perutz, as they too competed with Pauling in another arena: the molecular structure of various proteins.

For Kendrew however, this pursuit was not considered to be a competition against Pauling. Rather, he felt his corner of the laboratory to be working in tandem with researchers at Caltech in their joint pursuit of a common goal. For Kendrew, whoever got there first was beside the point. Indeed, when Perutz and Kendrew received the Nobel Prize for Chemistry – one year prior to Pauling’s receipt of his Peace Nobel – Kendrew credited Pauling as having been a source of inspiration and direction for his work on the atomic structure of myoglobin.

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John Kendrew and Max Perutz, 1962.

Sixteen years Pauling’s junior, John Cowdery Kendrew was born in Oxford, England on March 24, 1917. He received an appointment for study at Cambridge in 1939 and was working on reaction kinetics before the outbreak of World War II called him away to support the Allied effort.

By the time that he had reached the rank of Wing Commander in the Air Ministry Research Establishment, Kendrew had developed relationships with several important scientific contacts. Perhaps chief among these colleagues was the crystallographer J.D. Bernal, who also influenced Pauling’s protein work in the late 1930s. Bernal encouraged Kendrew to contact Max Perutz at the Cavendish Laboratory once his military service was completed. After receiving similar advice from Pauling, Kendrew began working with Perutz in 1945. His early research at the lab was conducted in support of his Ph. D. thesis – an x-ray diffraction study of hemoglobin in fetal and adult sheep.

In the late 1940s, Kendrew and Perutz established the Cavendish MRC Unit for the Study of the Molecular Structure of Biological Systems, and together they attacked the chemical structure of proteins using X-ray crystallography, with a particular interest in whale myoglobin. Although the research excited Kendrew, he was sometimes perplexed by the cross-disciplinary nature of what he was trying to accomplish. In a later interview with the Journal of Chemical Education, he remembered, “one of the problems was the lack of professional label. By profession, I was a chemist working on a biological problem in a physics lab.”

Nonetheless, Kendrew and Perutz were avidly pursuing the structure of keratin when the Pauling family visited the Cavendish in 1948. Pauling himself had done some preliminary work on the protein about ten years earlier, but after failing to build a satisfactory chain, he had abandoned the effort and moved on to other structures. Seeing the steady progress that Kendrew and Perutz were making reignited his own interest in the structure. Not long after, while lying in bed with a severe sinus infection, he worked on a rough sketch of a keratin model, which eventually inspired his signature proteins breakthrough: the alpha-helix.

Shortly after Pauling published his landmark 1951 paper, “The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain,” in which he introduced the alpha and gamma helixes, Pauling invited Kendrew to visit Pasadena and lecture at Caltech. Kendrew, impressed and eager to discuss Pauling’s findings, made preparations to stop in southern California as part of an already scheduled trip to San Francisco and Seattle. The visit proved thought-provoking for both scientists, and Kendrew returned to the Cavendish brimming with fresh ideas.

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Peter Pauling, 1954.

In their early exchange of correspondence, Pauling’s communications (as was typical) were usually formal and brief. On the contrary, Kendrew’s enthusiasm about both his and Pauling’s work is spelled out in long, detailed paragraphs. In due time, Pauling’s writing broadened not only in length, but in a personal dimension as well.  Importantly, between a letter dated October 8, 1956 and another written on November 22, 1957, Pauling switched from referring to his correspondent as “Dr. Kendrew” to “John,” and Kendrew responded in kind.

Without doubt, one catalyst for this shift was Kendrew’s mentorship and guidance of Linus’ second-oldest son, Peter Pauling, a budding crystallographer who was pursuing his doctorate at the Cavendish. Despite his promise and pedigree, once Peter had settled in, many scientists at Cambridge had begun to express concern about his level of commitment to and interest in his work.

Amidst a flurry of letters from Peter’s Cambridge professors that ranged from outright condemnation of his behavior to genuine concern for his future, a 1953 letter from Kendrew comes across as amiable but firm. In it, he expresses serious doubts about Peter’s ability to attain a Ph.D. unless he undergoes “a considerable revolution during the summer.” The message also urges the elder Pauling to alter other travel plans and come to England to address the matter in person. Ultimately, Pauling declined to do so and, fortunately, Peter initiated the revolution for which Kendrew had expressed hope. A year later, Kendrew penned another letter in which he assured Pauling that he had observed in Peter’s work both a genuine interest and a more stringent ethic.

Kendrew was not merely a fair-weather supporter of Peter’s endeavors. When Peter ran into serious personal trouble at Cambridge in 1955, Kendrew proved invaluably resourceful. Most notably, he helped Peter transfer his fellowship and remaining doctoral research to the Royal Institution of London, where former Cavendish chief Sir Lawrence Bragg was now directing the Davy-Faraday research lab.  Kendrew and Bragg later assisted Peter in moving yet again – this time to University College, London – when he could not complete his dissertation in the requisite amount of time allotted by the Royal Institution.

In a number of letters, Pauling repeatedly expressed his gratitude to Kendrew for so carefully tending to Peter’s well-being and educational progress, choppy though it was. These circumstances only served to cement a friendship between the two; one that developed alongside the great professional respect with which they had always extended to one another.

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Kendrew posing at a proteins conference held at Caltech, 1953.

On the other hand, Caltech and the Cavendish regularly found themselves to be in professional competition with one other, and this did lead to occasional friction between friends. In one instance, Kendrew sought out Pauling’s assistance with a rather complicated labor shortage that had partly been caused by Pauling himself. Shortly after Peter’s departure from Cambridge and Bragg’s resignation from his leadership post in the Cavendish, Kendrew wrote to Pasadena, asking for assistance. The gravity of the moment was especially amplified for Kendrew, who was presumably a tad annoyed by Pauling’s having convinced a mutual colleague, Howard Dintzis, to leave the Cavendish for Caltech the previous year. In his letter, Kendrew made a request:

I am writing to ask whether you would be good enough to let me know if you hear of any good man who would like to come to work on the myoglobin project in the near future. As you may have heard from Howard Dintzis, owing to a continuation of unforeseen circumstances I shall be totally without collaborators from January onward.

Pauling replied kindly, but did not include any recommendations.

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In 1957, Kendrew succeeded in delineating the atomic structure of myoglobin. Two years later, Max Perutz successfully mapped the structure of hemoglobin. When Lawrence Bragg approached Pauling with the idea of nominating Kendrew for the Nobel Prize in Chemistry, Pauling suggested that the award be split three ways between Kendrew, Perutz, and Robert Corey, a colleague of Pauling’s at Caltech. Bragg disagreed and instead nominated the British chemist Dorothy Crowfoot Hodgkin, a pioneer in X-ray crystallography. Ultimately, Pauling’s final nomination of Kendrew and Perutz in 1962 included Hodgkin as well. As it turned out, Kendrew and Perutz split that year’s prize, and Hodgkin took the 1964 award for herself.

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The remainder of Kendrew’s career was spent working less directly on scientific research and more intently on public policy. Like Pauling, Kendrew believed that scientists bore an obligation beyond scientific research and discovery. As he expressed in a 1974 interview

[Scientists] have special knowledge, and their most important responsibility is communication; because it is bad enough to try and foresee the effects of some scientific or technological advance given all the facts, but without them it is impossible…it is all the more important for scientists to communicate and make what they are doing understood at the government level and publicly through the media.

Wall of Honor at the European Molecular Biology Laboratory.

In the same year that he gave that interview, Kendrew helped to establish the European Molecular Biology Laboratory in Heidelberg, where he acted as director until his retirement in 1981. The lab has since created the John Kendrew Award to recognize and honor outstanding contributions made by the laboratory’s alumni.

Peter Pauling: Cambridge Struggles, 1954-1956

Julia and Peter Pauling, 1956.

[The life of Peter Pauling, Part 6 of 9]

The year 1954 was a tumultuous one for Peter Pauling. For one, Jim Watson had left for Caltech, and Peter lamented that his absence was felt, as he was “a positive force, albeit a bit conceited” when it came to social dynamics in the lab. At the same time, Peter’s sister Linda was preparing to move to Cambridge, where her father hoped that Peter might help her to find lab work assisting with crystal structure determinations. (Linda was quite interested in mathematics.) His sister’s imminent arrival excited in Peter visions of European exploration, and especially of skiing.

But while Peter dreamed, serious matters were afoot at the Cavendish Laboratory. Its director, Sir Lawrence Bragg, was planning to resign his Cambridge professorship to take a position as head of the Royal Institution in London. Meanwhile, the lab’s incoming director of physics, Nevill Mott, was widely known to be of the opinion that the unit’s increasing focus on biology needed to be redirected. John Kendrew was worried that the MRC unit that he and Max Perutz headed might be kicked out of the lab, or even the department, entirely.

This uncertainty both distracted Kendrew from Peter’s lack of progress on his myoglobin work, and, in retrospect, made Peter’s lack of enthusiasm for his topic all the more glaring. Indeed, while John Kendrew was worried about the future of their research, Peter was writing to his father that he was unconcerned about Mott’s approval. Rather, as was so often the case, Peter’s main preoccupation was his vehicle, this time a 1930 Mercedes Benz open touring car, described as “18 feet long and mostly engine,” that Peter was now cruising in for special occasions like the May Ball at Peterhouse. Peter’s older brother, Linus Jr., had forwarded him money to purchase the car, hoping that it would be affordable to rebuild the engine. When the cost of doing so turned out to double his investment in the vehicle, Linus Jr. thought it more expedient to simply let his younger brother have the car.

Linus Jr. and Peter formed a strong relationship during Peter’s years at Cambridge, a time period where Linus Jr. and his wife Anita made a habit of travelling around Europe during the summers. This closeness marked something of a renewal of the brothers’ relationship since they had seen little of one another during their more formative years, and as children had little in common. Now, cars in particular emerged as an area in which the two could share their exuberance. Linus Jr. reflected later that, on those trips abroad, he and his wife enjoyed Peter tagging along – his vitality, beaming smile, and friendly nature made him the life of any party.

But this was clearly only one side of Peter Pauling. Privately, he admitted to his mother that he often felt unsure of his path in life, and that he felt unable to meet the challenges of his PhD program. He often wondered whether or not he would be better off simply teaching chemistry, or helping to write his father’s textbooks. These bouts with gloom were contrasted by sudden and excited turns to sociability. Linus Jr. would later point out that their paternal grandmother – Linus Pauling’s mother, Belle – was possibly manic depressive, and was reported to have died in a mental hospital. This, he believed, was likely where Peter had inherited his own emotional instability, and it was during his stint in Cambridge that manic depressive symptoms started to manifest most clearly.

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The Paulings in Stockholm, December 1954. Credit: Svenskt Pressfoto.

Linus Pauling’s frustration with Peter’s hoax “Francis Crick letter” had faded by the time that the entire family met in Stockholm for the 1954 Nobel Prize ceremonies. It was there that Pauling was to receive his highest honor to date, the Nobel Prize for Chemistry, commemorating his work on the nature of the chemical bond. After a frustrating battle to receive government permission to leave the country – by then, Linus’ political activities were causing him problems with the Passport Office – the Pauling family flew to Copenhagen where they met Peter and Linda. By then, Linda had taken up residence in the basement room that her brother had just left at the “Golden Helix,” as the Crick home on Portugal Place was now known. Once arrived, she worked for a time as Francis and Odile Crick’s au pair.

Watson returned to the Cavendish in 1955 to find the MRC unit on the verge of being squeezed out by Nevill Mott. Finally registering this threat, Peter began to panic, writing to implore his father that he vocalize his positive impressions of the unit’s work and that he recommend that the group be allowed to continue their research there. At the same time, Peter applied for a post-doctoral fellowship grant from the National Science Foundation, hoping to solidify the standing of both himself and the group by bringing additional research money into the lab.

As it turned out, Peter’s maneuver worked: he received the grant, and this was no doubt a boon to his position at a crucial time. It did little to help him in his research, however. He continued to struggle with myoglobin and, increasingly, he placed his fading hopes squarely upon the idea that mercuric tetraiodide ion crystals might be a better candidate for the sorts of analysis that Kendrew and Perutz were beginning to doubt he could complete.

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As the final year of Peter’s program dawned in fall 1955, the frequency of his drives about the grounds to impress the girls dropped to what Jim Watson considered a startlingly low level. Perhaps realizing the “do or die” position that he was in with respect to his research, Peter seemed to be redoubling his focus on finishing his degree.

During this same period, Peter had begun seeing a young woman by the name of Julia, who was a student at a nearby all-women’s school. Jim Watson, curious about the situation, queried several girls that he knew from the school, but most were silent, and Julia herself became conspicuously absent as the New Year drew closer.

Meanwhile, Peter’s father had been working to prepare his son for life after Cambridge, offering him an appointment in the Caltech Division of Chemistry and Chemical Engineering as a Research Fellow focusing on the crystalline structure of globular proteins, to be determined through the use of x-ray diffraction. Pauling wrote to his son

We have a real need here for someone who has had the sort of experience in taking x-ray photographs of crystals that you have obtained. I think our effort to determine the complete structure of a crystalline globular protein is going to be successful, and that you might like to be associated with the successful effort.

Peter did not respond immediately, taking about a week to think about the proposal. It may well be that he was simply overwhelmed by both the work to be done and the festivities to be had during his final months at Cambridge. Plus, it seemed that the job his father had offered likely would be waiting for him as soon as he had finished his program in England.

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Few had seen much of Peter in the run-up to Jim Watson and Linda Pauling’s practical joke of a dinner party. In response to a rumor that Watson and Linda were seeing one another, the two decided in good fun to host a get-together, thus driving speculation into a frenzy by implying an impending announcement that, in fact, was never to come. Peter was invited and did show up, but much to the surprise of the hosts, he was not his usual grinning, charming self. Instead, he seemed sentimental and full of a solemn interest in the future of his friends at Cambridge. Watson and Linda later realized that, on this particular evening, Peter was wrestling with a weighty issue: he was soon to become a father.

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The Pauling family on Christmas Day, 1956. Peter and Julia sit at right.

A letter sent by Peter’s parents in early 1956 concluded with an expression of excitement: Linus and Ava Helen would be visiting soon and would look on with pride as they witnessed their son receiving his Cambridge Ph.D. In his response, Peter explained that this day, sadly, would never come. Though he felt that she was a “clever, delicate, and lovely girl,” Peter had not made Julia an “honest woman,” and for this he would be sent down from Cambridge and not be allowed to take a degree. Accordingly, this also meant that he would not qualify for the position that his father had offered him at Caltech.

When he learned of his situation, John Kendrew suggested that Peter might be able to transfer both the remainder of his fellowship with the National Science Foundation, and also the completion of his doctoral research, to the Royal Institution in London, where Sir Lawrence Bragg – his old program director at the Cavendish – was now director of the Davy-Faraday research lab. By then, however, Peter had decided to marry the mother of his child, and arrangements were quickly made by Linda Pauling for a quiet civil wedding that was out of the spotlight and not attended by Linus or Ava Helen.

Peter and Julia were married on March 13, 1956 at the Cambridge Register Office on Castle Hill. Peter’s bride was given away by her father, and with no family members other than Linda present, Peter’s sister acted as the sole adjudicator of the Pauling family’s approval of the union. Peter’s Cambridge advisor, John Kendrew, stood with him as his best man. Following the wedding, a reception was held at Kendrew’s home at Tennis Court Road, after which Peter put on his trademark grin and, with Julia, vanished in a new Porsche. Before the year was out, Linda Pauling, struggling financially and burdened by an expired work visa, returned to Pasadena.

Between 1957 and 1959, Kendrew and Perutz successfully modelled the molecular structure of myoglobin that Peter had been working on. In this, the Cavendish once more beat Caltech to the punch, as the position that Linus had offered to Peter was meant to contribute to a similar problem. Myoglobin was the first ever protein to have its atomic structure determined, and Kendrew and Perutz shared the Nobel Prize in chemistry for this achievement in 1962.

Peter Pauling at Cambridge, 1953-1954

Peter Pauling, 1954.

[The life of Peter Pauling, part 5 of 9]

In the first months of 1953, with his office mates scrambling to determine the molecular structure of DNA before his own father could beat them to it, Peter Pauling was mostly concerned with the English weather. He had been at Cambridge University since the fall of 1952 when he began his PhD program in physics at the university’s Cavendish Laboratory, and in that time he judged that he had seen a mere two full days of sun and was now officially fed up.

His father, by contrast, was mostly concerned with finishing his most recent edition of The Nature of the Chemical Bond, for which he had often solicited Peter as a source to provide example problems and solutions prior to his departure for England. As he was now beginning his graduate research, however, Peter was too busy to provide much assistance for this edition.

Instead, he was mostly occupying himself with a muscle camera developed by Hugh E. Huxley, a molecular biologist studying the physiology of muscle with Max Perutz’ Medical Research Council (MRC) Unit of Molecular Biology at Cambridge. Taking pictures of fibrous and globular proteins – beginning with insulin and tropomyosin – Peter applied the Cochran-Crick theory, with the goal of determining the helical structure of these protein molecules. This inquiry was, in principle, made possible by Linus Pauling’s work from less than a decade prior.

Since 1947, when the MRC unit was founded by Sir Lawrence Bragg, John Kendrew and Max Perutz had endeavored to use x-ray crystallography to determine the molecular structure of hemoglobin in sheep. By the time that Peter arrived at Cambridge, however, hemoglobin had proven to be an untenable object of study, and Kendrew’s focus had shifted to myoglobin. Whereas hemoglobin is found mostly in the blood, myoglobin is generally found only in muscle tissue. Both are proteins that carry oxygen to cells. Problematically, myoglobin is one fourth the size of hemoglobin, and too small for the era’s techniques of x-ray analysis.

To solve this issue, sperm whale myoglobin was used in hopes that the molecular details of the larger, oxygen-rich proteins of a diving mammal would be more observable with the tools then available. “Stranded whales are the property of the Queen,” Peter explained to his father as he discussed this work, “but we have an agreement with her to get a piece of meat if one comes ashore.” Nonetheless, though availed of samples from beached whales in the United Kingdom and from countries as far afield as Peru, Kendrew could not render the x-ray diffraction patterns with complete certainty.

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Sperm whale myoglobin image created by John Kendrew.

In 1953, Perutz realized that by comparing the diffraction patterns of natural whale myoglobin crystals to crystals soaked in heavy metal solutions – a procedure called multiple isomorphous replacement – the positions of the atoms in myoglobin could be more accurately determined. Accordingly, Peter was tasked with making countless measurements in support of this effort.

Peter wrote to his father often over the next two years as he struggled to complete this project, which was the focus of his PhD. In particular, Peter asked for advice on how one might best get heavy metal atoms onto myoglobin, detailing his attempts to use everything from saltwater to telluric acid, which was used to produce salts rich in metallic contents, such as the element Tellurium.

Indeed, Peter’s work proceeded slowly, not least of all because of his knack for keeping things entertaining. Shortly after Watson and Crick’s discovery of DNA, for example, he fabricated a letter of invitation from his father, Linus Pauling, to Francis Crick, requesting Crick’s presence at an upcoming conference on proteins at Caltech. “Professor Corey and I want you to speak as much as possible during the meeting,” the impostor Pauling said to Crick in the fake letter, even urging him to consider lecturing at Caltech as a visiting professor. Linus Pauling had appeared to sign the letter himself, his signature skillfully forged. The letter proved so convincing that Crick actually replied, accepting the invitation to speak at the conference.

Before long, it became apparent that the entire communication was, in fact, a practical joke. Lawrence Bragg, the director of the Cavendish Laboratory, where Crick himself worked, was scheduled to speak at the proteins conference in the same time slot that the fake letter had proposed for Crick. Were it not for this, the deception might have gone even farther, since upon seeing his son’s forgery Linus himself was almost convinced that he had written the letter and had simply forgotten about it amidst the relentless pace of his schedule.

Ever a stickler for the details, however, Pauling noticed a grammatical error in the document that he would never have made. From there, he deduced the letter as having been authored by his mischievous son. For this transgression, Linus subtracted a five-pound fine from the $125.00 check that he sent to Peter each month.

The Iron-Oxygen Bond in Oxyhemoglobin

Pastel drawing of the hemoglobin molecule by Roger Hayward, 1964.

Part of the beauty of studying the life and work of Linus Pauling is that doing so often affords the opportunity to look at how the science of today has developed from questions that were once unanswered and widely debated. One such question was how hemoglobin, the protein in red blood cells, binds to and releases oxygen as it is inhaled and carried to the body’s tissues.

In 1959, Max Perutz used x-ray crystallography to obtain an image of oxyhemoglobin, a hemoglobin protein bound to an oxygen molecule. This was a major breakthrough in many ways. For one, it allowed chemists to observe an image of a three-dimensional protein found in humans for the first time. The imagery also provided tantalizing hints about the specific chemistry that might explain oxyhemoglobin’s structure.

Unfortunately, creating an image of the molecular structure didn’t solve everything, as Perutz himself would reflect in a 1978 article, “Hemoglobin Structure and Respiratory Transport.”

We were like explorers who have discovered a new continent, but it was not the end of the voyage, because our much-admired model did not reveal [hemoglobin’s] inner workings.

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The Joseph Weiss Medal, which commemorates his work as a radiation chemist.

Perutz’s work naturally incited biochemists to further explore the structure of hemoglobin. While it was known that the oxygen-carrying heme group in hemoglobin is composed of nitrogen, carbon, and an oxygen-binding iron, there was much debate over what kind of bond could cause the union and dissociation of these elements.

In 1964, Joseph Weiss, a professor at Newcastle University in England, attempted to answer the question of what specific bond forms between iron and oxygen. Weiss’s conclusions were published in a 1964 article, “Nature of the Iron–Oxygen Bond in Oxyhæmoglobin”.

According to Weiss, the iron in hemoglobin would need to be in the ferric state (iron with an ionic charge of +3) in order to account for hemoglobin’s behavior in oxygen transport.  He believed that ferric iron would also explain hemoglobin’s spectroscopy (the wavelengths of light reflected by a  molecule). Pauling, however, disagreed with Weiss.

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Pauling, Max Delbruck and Max Perutz, 1976.

Interestingly, Pauling had been looking into the subject of the iron-oxygen bond in hemoglobin since 1948, when he presented a paper titled “The Electronic Structure of Hemoglobin” at a symposium in Cambridge, England. Pauling’s presentation considered advances in x-ray diffraction and quantum mechanics to propose a structure for the heme group in the protein. Unlike Weiss, Pauling believed that the iron-oxygen bond in oxyhemoglobin would require ferrous iron (an iron with an ionic charge of +2) to form a double bond (a bond involving two electrons) with oxygen as it was being transported throughout the body.  Weiss’s paper did little to change Pauling’s mind on the subject.

In 1964, Pauling wrote “Nature of the Iron–Oxygen Bond in Oxyhæmoglobin,” a direct response to Weiss’s article with the same title. In it, Pauling stated

I conclude that oxyhæmoglobin and related hæmoglobin compounds are properly described as  containing ferrous iron, rather than ferric iron, that their electronic structure involves essentially the formation of  a double bond between the iron atom and the near-by oxygen atom in  oxyhæmoglobin

Pauling’s interest in the components of blood had emerged early on in his career. In 1948 he suggested using hemoglobin to test his earlier ideas about bonds that had remained unexplored, as the structure of the protein had been hitherto not fully understood. This was a pursuit that he in which he strongly believed: in his Cambridge talk, “The Electronic Structure of Hemoglobin,” he had concluded that

even the great amount of work that would be needed for a complete determination of [hemoglobin’s] structure, involving the location of each of the thousands of atoms in its molecule, would be justified.

Many years later, in his 1992 article “The Significance of the Hydrogen Bond,” Max Perutz stated that that Pauling’s words, as published in 1949, were among the inspirations propelling his own work a decade later.

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“The Electronic Structure of Hemoglobin” wasn’t the only publication by Pauling that inspired Perutz. In 1970, he used Pauling’s “The Magnetic Properties and Structure of Hemoglobin” to further his own study of the structure of hemoglobin, work which finally led to the discovery that the iron-oxygen binding in hemoglobin depends on the electronic spin transition of the iron atom.

Essentially, Perutz found that when the ferrous iron in hemoglobin is in a low spin state, its higher d-orbitals are unoccupied by electrons, which allows oxygen to form a bond with iron. In a high spin state, the electrons in ferrous iron are occupying all d-orbitals in the atom and oxygen remains unbound.

This suggests that the more likely structure for hemoglobin involves a single bond between iron and the oxygen molecule, not the double bond that Pauling had proposed in 1948 and again in 1964.  But Pauling was correct with respect to the presence of ferrous iron in the compound, and he had been able to make this determination before any crystallographic pictures were available to him.

 

Pauling and Perutz: The Later Years

[Concluding our series on Max Perutz, in commemoration of the Perutz centenary.]

In 1957, Max Perutz and Linus Pauling wrote to each other again on a topic that was new to their correspondence. This time Pauling asked Perutz to sign his petition to stop nuclear weapons tests, a request to which Perutz agreed.

Signature of Max Perutz added to the United Nations Bomb Test Petition, 1957.

As the decade moved forward, the discovery of the double helical structure of DNA attracted ever more attention to the work of James Watson and Francis Crick. In May 1958, Perutz asked Pauling to sign a certificate nominating his colleagues Crick and John Kendrew to the Royal Society. Pauling agreed, though stipulated that Kendrew’s name be placed first on the nomination, as he expected that Crick would get more support. As with Pauling’s bomb test petition a year earlier, Perutz agreed.

At the beginning of 1960, William Lawrence Bragg wrote to Pauling about nominating Perutz, along with Kendrew, for the 1961 Nobel Prize in Physics. Pauling was hesitant about the nomination, thinking it was still early, as their work on hemoglobin structure had only recently been published. Pauling also felt that Dorothy Hodgkin should be included for her work in protein crystallography. Bragg thought this a good idea and included Hodgkin in his nomination.

By March, Bragg’s nominations had gone through and Pauling was asked to supply his opinion. After spending some time thinking about the matter, Pauling wrote to the Nobel Committee that he thought that Robert B. Corey, who worked in Pauling’s lab, should be nominated along with Perutz and Kendrew for the Nobel Prize in Chemistry instead. Pauling felt that if Perutz and Kendrew were included in the award, Corey should be awarded half, with the other half being split between Perutz and Kendrew. Pauling also sent a letter to the Nobel Committee for Physics, indicating that he thought that Hodgkin, Perutz, and Kendrew should be nominated for the chemistry prize. Pauling sent a copy of this letter to Bragg as well.

Pauling’s letter to the Nobel Committee, March 15, 1960. pg. 1.

Pg. 2

In July, Bragg replied to Pauling that he was in a “quandary” about Corey, as he was “convinced that” Corey’s work “does not rank in the same category with that which Mrs. Hodgkin or Perutz and Kendrew have done.” Perutz and Kendrew’s efforts, he explained, had theoretical implications directly supporting Pauling’s own work, whereas Corey’s research was not that “different from other careful analyses of organic compounds.” Once everything was sorted out, Perutz and Kendrew were awarded the Nobel Prize for Chemistry in 1962 (the same year that Watson and Crick, along with Maurice Wilkins, won in Physiology/Medicine, and Pauling, though belated for a year, won the Nobel Peace Prize) and Hodgkin received the Nobel Prize for Chemistry in 1964. Robert Corey never was awarded a Nobel Prize.

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Linus Pauling, Max Delbrück and Max Perutz at the American Chemical Society centennial meeting, New York. April 6, 1976.

Perutz and Pauling corresponded very little during the 1960s, with Perutz writing only to ask for Pauling’s signature, once for a photograph that would be displayed in his lab and a second time for a letter to Italian President Antonio Segri in support of scientists Domenico Marotta and Giordano Giacomello, who were under fire for suspected misuse of funds.

In 1971 Perutz read an interview with Pauling in the New Scientist which compelled him to engage Pauling on scientific questions once again. Perutz was surprised to have read that Pauling had tried to solve the structure of alpha keratin as early as 1937 and that his failure to do so led him to study amino acids. Perutz wrote that had he known this in 1950, he, Bragg and Kendrew might not have pursued their own inquiry into alpha keratin. Pauling responded that he thought his efforts had been well-known as he and Corey had made mention of them in several papers at the time. Pauling explained that he had difficulties with alpha keratin up until 1950, when he finally was able to show that the alpha helix best described its structure. Perutz replied that he was aware of Pauling and Corey’s work and the alpha helix, but was surprised that Pauling’s early failure to construct a model led him to a more systematic and fruitful line of research.

Perutz also wondered whether Pauling had seen his article in the previous New Scientist, which reflected on Pauling and Charles Coryell’s discovery of the effect of oxygenation on the magnetic qualities of hemoglobin. Perutz saw this as providing “the key to the understanding of the mechanism of haem-haem [heme-heme] interactions in haemoglobin.” Pauling responded that he had not seen Perutz’s article but would look for it, and also sent Perutz a 1951 paper on the topic. Perutz took it upon himself to send Pauling his own article from the New Scientist.

A few years later, in 1976, Perutz again headed to southern California to attend a celebration for Pauling’s 75th birthday, at which he nervously gave the after dinner speech to a gathering of 250 guests. Before going to the event in Santa Barbara, Perutz stopped in Riverside and visited the young university there, which impressed him. Perutz wrote to his family back in Cambridge that he wished that “Oxbridge college architects would come here to learn – but probably they wouldn’t notice the difference between their clumsy buildings and these graceful constructions.”

Perutz also visited the Paulings’ home outside Pasadena, which elicited more architectural comments. Perutz described to his family how the Pauling house was shaped like an amide group, “the wings being set at the exact angles of the chemical bonds that allowed him to predict the structure of the α-helix.” Perutz asked Pauling, perhaps tongue in cheek as he thought the design somewhat conceited, “why he missed the accompanying change in radius of the iron atom.” Pauling replied that he had not thought of it.

Bertrand Russell and Linus Pauling, London England. 1953.

In preparation for his speech, Perutz also took some time to read No More War! which he concluded was as relevant in 1976 as when it was first published in 1958. Perutz saw Pauling’s faith in human reason as reminiscent of Bertrand Russell’s. Indeed, the many similarities between the two were striking to Perutz, and he included many of them in his talk, “except for their common vanity which I discreetly omitted.” In a personal conversation, Perutz asked Pauling about his relationship with Russell which, as it turned out, was mostly concerned with their mutual actions against nuclear weapons. Perutz was somewhat disappointed that “they hardly touched upon the fundamental outlook which I believe they shared.”

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Perutz and Pauling were again out of touch for several years until April 1987, when Pauling traveled to London to give a lecture at Imperial College as part of a centenary conference in honor of Erwin Schrödinger. Pauling’s contribution discussed his own work on antigen-antibody complexes during the 1930s and 1940s, during which he shared a drawing that he had made at the time. Perutz was in attendance and noticed how similar Pauling’s drawing was to then-recent models of the structure that had been borne out of contemporary x-ray crystallography. Perutz sent Pauling some slides so that he could judge the similarities for himself.

Flyer for Pauling’s 90th birthday tribute, California Institute of Technology, February 28, 1991.

The final time that Pauling and Perutz met in person was for Pauling’s ninetieth birthday celebration in 1991. Perutz, again, experienced stage fright as he gave his speech. But he was encouraged afterwards, especially after receiving a compliment from Francis Crick who, according to Perutz, was “not in the habit of paying compliments.” Perutz told his family that the nonagenarian Pauling “stole the show” by giving one speech at 9:00 AM on early work in crystallography and then another speech at 10:00 PM on his early years at Caltech. Perutz found it enviable that Pauling stood for both lectures and was still getting around very well, though he held on to the arm of those with whom he walked. Without coordinating, Perutz and Pauling also found a point of agreement in their talks, noting that current crystallographers were “so busy determining structures at the double” that they “have no time to think about them.” This rush often caused them to miss the most important aspects of the newly uncovered structures.

Just as Perutz first encountered Pauling through one of his books, The Nature of the Chemical Bond, so too would Pauling’s last encounter with Perutz be through a book, Perutz’s Is Science Necessary? Pauling received the volume in 1991 as a gift from his friends and colleagues Emile and Jane Zuckerkandl. Pauling’s limited marginalia reveal his interest in the text’s discussions of cancer and aging research. Aged 90 and facing his own cancer diagnosis, Pauling was particularly drawn to Perutz’s review of François Jacob’s The Possible and the Actual which sought, but did not find, a “death mechanism” in spawning salmon. Pauling likewise highlighted the book’s suggestion that “like other scientific fantasies…the Fountain of Youth probably does not belong to the world of the possible.” And Pauling made note of particular individuals that he had known well, like John D. Bernal and David Harker. Pauling deciphered the latter’s identity from Perutz’s less-than-favorable anonymous portrayal.

Pauling also noted spots where Perutz wrote about him. While most of these references were positive and focused on topics like Pauling’s influence on Watson and Crick and his breakthroughs on protein structure, one in particular was not. Perhaps less cryptic than the reference to Harker, Perutz described how “one great American chemist now believes that massive doses of vitamin C prolong the lives of cancer patients,” following it with “even more dangerous are physicians who believe in cancer cures.”

While critical, Perutz really meant the “great” in his comment and he continued to repeat it elsewhere. After Pauling passed away in August 1994, Perutz told his sister Lotte that “many feel that he [Pauling] was the greatest chemist of this century” while also being “instrumental in the protests that led to Kennedy and Macmillan’s conclusion of Atmospheric Test ban.”  He reiterated this idea in the paragraph that concluded his obituary of Pauling, published in the October 1994 issue of Structural Biology.

Pauling’s fundamental contributions to chemistry cover a tremendous range, and their influence on generations of young chemists was enormous.  In the years between 1930 and 1940 he helped to transform chemistry from a largely phenomenological subject to one based firmly on structure and quantum mechanical principles.  In later years the valence bond and resonance theories which formed the theoretical backbone of Paulings work were supplemented by R. S. Mullikens’ molecular orbital theory, which provided a deeper understanding of chemical bonding….Nevertheless resonance and hybridization have remained part of the everyday vocabulary of chemists and are still used, for example, to explain the planarity of the peptide bond.  Many of us regard Pauling as the greatest chemist of the century.

Pauling and Perutz in the Golden Age of Protein Research

Max Perutz, 1987. Image Credit: Graham Wood.

[Part 3 of our series celebrating the Perutz centenary.]

In 1939 Max Perutz’s girlfriend gave him a book token for Christmas. Working on finishing his dissertation on the structure of hemoglobin, Perutz used that token to purchase Linus Pauling’s recently published text, The Nature of the Chemical Bond.

In the obituary of Pauling that he wrote some fifty-five years later, Perutz described how the “book transformed the chemical flatland of my earlier textbooks into a world of three-dimensional structures” and “fortified my belief, already inspired by J. D. Bernal, that knowledge of three-dimensional structure is all-important and that the functions of living cells will never be understood without knowing the structures of the large molecules composing them.”  The purchase of Pauling’s book marked the beginning of a long, fruitful and sometimes contentious correspondence between the two men, working on separate continents but united by similar interests.

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Not until 1946 did Perutz first write to Pauling, asking for assistance as he labored through his research on the structure of hemoglobin. The Cavendish Laboratory, where Perutz was located, did not have the latest equipment that was available to Pauling at Caltech. In particular, Perutz needed a Hollerith punch-card machine to carry out calculations of the three-dimensional Patterson-Fourier synthesis. Perutz knew that Pauling’s lab was already conducting calculations of this sort and that the work Perutz was doing “would have to be done sooner or later, if the molecular structure of the proteins is to be worked out.”

As such, Perutz hoped that someone in Pauling’s lab might do the calculations for him. Pauling was not moved enough by Perutz’s request to offer the labor of his own team, replying that enlisting someone do such work in a “routine way” could lead to confusion. Pauling did offer that Perutz come to Pasadena, or send a surrogate to do the work, if he could find the money. Perutz was unable to support such an undertaking and so ended that conversation.

Linus Pauling and Lord Alexander R. Todd. Cambridge, England. 1948.

Two years later, in 1948, Pauling was in England, enjoying a stint as George Eastman Professor at Oxford. It was during this time that he and Perutz met for the first time in person. Perutz described his first experiences of Pauling’s lectures, in which

he would reel off the top of his head atomic radii, interatomic distances and bond energies with the gusto of an organist playing a Bach fugue; afterwards he would look around for applause, as I had seen Bertrand Russell do after quoting one of his eloquent metaphors.

The two also found time to talk together about their own particular research projects.

Pauling’s work at Oxford touched directly on Perutz’s own program, in what would become a oft-noted story in twentieth century history of science. As Pauling lay in bed with a cold, he did not stop working, choosing to spend his time making planar peptide models with paper chains. From his paper folding exercises, Pauling, according to Perutz’s obituary, “found a satisfactory structure by folding them into a helix with 3.6 residues per turn.” (A story that Pauling relayed many times himself.) The structure would come to be known as the alpha helix.

After Pauling recovered from his illness, Perutz showed him his own model of a polypeptide chain which was part of his larger hemoglobin model and was similar to fibers described by William Astbury. To Perutz’s “disappointment, Pauling made no comment,” and gave no hint as to his own breakthrough, which he announced the next year in a “dramatic lecture.”  That later unveiling of the alpha helix gave rise to a famous Perutz anecdote, which later informed the title of a book of essays that Perutz published.

When I saw the alpha-helix and saw what a beautiful, elegant structure it was, I was thunderstruck and was furious with myself for not having built this, but on the other hand, I wondered, was it really right?

So I cycled home for lunch and was so preoccupied with the turmoil in my mind that I didn’t respond to anything. Then I had an idea, so I cycled back to the lab. I realized that I had a horse hair in a drawer. I set it up on the X-ray camera and gave it a two hour exposure, then took the film to the dark room with my heart in my mouth, wondering what it showed, and when I developed it, there was the 1.5 angstrom reflection which I had predicted and which excluded all structures other than the alpha-helix.

So on Monday morning I stormed into my professor’s office, into [William Lawrence] Bragg’s office and showed him this, and Bragg said, ‘Whatever made you think of that?’ And I said, ‘Because I was so furious with myself for having missed that beautiful structure.’ To which Bragg replied coldly, ‘I wish I had made you angry earlier.’

 

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Once Pauling returned to Pasadena, he and Perutz fell into a minor quarrel. In December 1950, Perutz had heard that Pauling had been “annoyed” by Perutz and John Murdoch Mitchison’s paper, “State of Hæmoglobin in Sickle-Cell Anæmia,” which had been published in Nature that October. Pauling was upset that Perutz and Mitchison had suggested that crystallization caused cells to sickle without properly citing his own seminal work on the subject.

In a December letter, Perutz said he was “very disappointed” that Pauling was upset with the publication, not only because there was a reference to Pauling, et al. in its introductory paragraph, but “particularly because all the new experimental evidence we report seemed to fit in so beautifully with the basic ideas set out in” Pauling’s co-authored Science article, “Sickle Cell Anemia, a Molecular Disease,” published in November 1949. Perutz explained his position in more detail, noting,

There is perhaps a slight difference between our points of view. Whereas you regard the sickling as being due to an aggregation and partial alignment of hæmoglobin molecules by a lock and key mechanism, an interlocking of specific groups in neighbouring molecules, we regard the cause of the sickling as being simply a crystallization, due to abnormally low solubility of the reduced hæmoglobin. No specific interaction of the kind you mention need be involved in the second process, though it obviously may be…I am sorry that this misunderstanding between us should have arisen, particularly as I have spent much effort trying to convert unbelievers to your scheme.

Pauling waited until the following February to respond and explained his feeling that readers of Perutz’s article might conclude that Perutz was making an original proposal. Having made this statement, Pauling, in his own way, moved beyond the quarrel by telling Perutz about his more recent work showing that “hemoglobin is not crystallized in the sickle cells, but is only converted to the nematic [or liquid crystal] state.” The ice broken, Perutz quickly responded by inviting Pauling to take part in informal discussions about protein structure at the Cavendish Laboratory before an annual conference, to be held in Stockholm. Pauling, however, could not attend.

The next year, Pauling attempted to visit England, this time to speak at a conference about the alpha helix, but was delayed due to his passport renewal being denied on account of his political activities. Perutz wrote that Pauling’s “absence had a sadly damping effect on our meeting at the Royal Society, and it made the discussion rather one sided as there was no none to answer the various objections to the α-helix raised by the Astburites and Courtlauld people” since Pauling’s supporters were unprepared to defend Pauling’s position without him. Perutz was also keen to show Pauling his own progress, an eagerness that Pauling reciprocated. By July Pauling had cleared up his passport problems and was able to spend time in person discussing his and Perutz’s work.

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By 1953 Perutz and Pauling were quarrelling again over proper citation, though this time it was Perutz suggesting that Pauling had not given Francis Crick enough credit regarding the coiling of alpha helixes. Pauling explained to Perutz that, while he was at Cambridge the previous summer, he had talked with Crick and John Kendrew at length. During that conversation, according to Pauling,

There was only brief discussion of α keratin at this time, and, if my memory is correct, only a few sentences were said about the coiled coil, as Crick calls it. We discussed the fact that the 5.15-Å meridional reflection offers some difficulties of explanations, and that also there seemed to be a discrepancy in the density of α keratin. The discussion was very brief. Then Mr. Crick asked me if I had ever thought of the possibility that the α helixes were twisted about one another. I answered that I had. So far as I can remember, nothing more was said on this point.

Pauling went on to emphasize that “the idea was not a new one to me then” and that his own description of it in Nature was different from Crick’s understanding. Perutz ceded this point, adding that Pauling’s differences with Crick “stimulated Crick to clarify his own” ideas on the coiling of alpha helixes. More generally, Perutz found that the competition that arose between the two labs as they worked on similar problems helped to push each forward, thus leading to positive advances.

The famous group photo of the Pasadena Conference on the Structure of Proteins, September 1953. Pauling stands front row, third from left. Perutz stands two rows behind Pauling. [Image credit: The Archives, California Institute of Technology]

That September, Perutz made his first visit to California in order to deliver a paper at the Pasadena Conference on the Structure of Proteins, at which were gathered all of the world’s major figures in the field, including Jim Watson and Francis Crick, newly famous for their double helical structure of DNA. Perutz told his wife, Gisela, that his paper was “well received.” Additionally, with all of the different perspectives presented, there was “an atmosphere of soberness, and a realization that no-one’s solution of the protein problem was complete, and every approach was still fraught with complications.” Perutz was also quite taken with the Paulings’ home and their hospitality, pointing out that Ava Helen had invited him “after one of the meetings for a swim in their garden.”

Correspondence between Perutz and Pauling dipped a bit after the conference, though Pauling did take a moment to congratulate Perutz on being elected to the Royal Society the following Spring. While the exchange was brief, it reflected the long relationship built up between the two over the preceding years and, in particular, a confluence of work that had boosted the esteem of both scientists.

Perutz had begun looking at the structure of wool proteins back in 1951, thinking that there might be similarities to hemoglobin. He became excited after finding Pauling’s work on alpha helixes in fibers, thinking that the structure might be present in wool as well. His initial studies resulted in disappointment, but after adjusting the angle at which he was taking his x-rays by 30 degrees, he compiled new data that confirmed Pauling’s alpha helix structure. After applying it to his own work on hemoglobin, Perutz told Pauling “the discovery of this reflexion in haemoglobin has been the most thrilling discovery of my life…there is no doubt that it is a universal feature at least of all fibers of the α type. Whether all crystalline proteins show it remains to be seen.” Not suprisingly, Pauling was also “very pleased” with this discovery.

This research opened the door for Perutz to be considered by the Royal Society. But it was his development of a technique for determining a three-dimensional view of structures derived from x-ray crystallography that assured his election. He did this be attaching mercury atoms to hemoglobin, which allowed him to figure out where the crest and trough of a given x-ray was in relation to the structure that appeared on the photos. Perutz later said that after he finished the work and published it in Nature at the end of 1959, he went skiing in the Alps, and by the time he returned he was famous, assuring his fellowship in the Royal Society.

Perutz’s Hemoglobin Breakthroughs and Later Work

Perutz with his hemoglobin molecule, 1959. Image credit: Life Sciences Foundation.

[Part II of our survey of the life of Max Perutz, this time focusing on the years 1941-2002. Published in commemoration of the Perutz centenary, May 2014.]

Knowing that his parents were safe from Nazi persecution and able to return to the United States, circumstances began improving for Max Perutz. The Rockefeller Foundation reactivated his grant, allowing him to support himself while stateside as well as his parents in Cambridge, England. Perutz’s father was also able to find work as a laser operator during the war and afterwards qualified for a pension.

In September 1941, Perutz met Gisela Peiser, who was an accountant at the Society for the Protection of Science and Learning, an organization that assisted Jewish and other academic refugees fleeing from the Nazis. After a quick courtship, they were married the following March and, in December 1944, welcomed their daughter Vivien into the world. That same year, Perutz also found himself back in good stead with the British government and recruited to research ice strength for potential ice stations in the North Atlantic. The research did not work out, so Perutz returned to his work on hemoglobin at Cambridge. The next few years were spent trying to put together a secure source of income for him and his growing family. In the interim, he took out more loans and found a temporary fellowship.

Meanwhile, Perutz’s health continued to suffer. As his chronic gastrointestinal attacks became more unbearable, interfering with his daily activities more and more, Perutz began to seek out help. Most doctors he saw told him it was a psychological problem, but eventually one doctor recognized that the symptoms could be treated by a mixture of atropine and codeine. The remedy helped enough for Perutz to live more or less undisturbed by the problem for several years, though eventually that would change.

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Perutz and John Kendrew, 1962. Image credit: Nobel Foundation.

In 1947, the war now completed, Perutz, along with John Kendrew, was appointed to head the new Research Unit for the Study of the Molecular Structure of Biological Systems (Perutz later shortened the unit’s name to Molecular Biology Research) at the recently established Medical Research Council. Situated at the Cavendish Laboratory in the physics department, the group expanded on Perutz’s earlier application of x-ray crystallography to biological materials. Perutz, in this new administrative role, described his lab management as one where he would “leave people free to do what they wanted…if they were good scientists.”

One of the several student researchers that came through the lab was Francis Crick, who started work in 1949. Perutz had Crick look at the validity of his hemoglobin model, which was the culmination of roughly six years of research. Crick applied his mathematical training to show that the model was “nonsense.” Perutz accepted Crick’s assessment and later reflected that only in England at that time could a student be so critical of their principal investigator. Crick was eventually drawn away from hemoglobin research by James Watson, who came to the lab in 1951 to work under Kendrew on molecular structure, but his impact on the development of Perutz’s hemoglobin structure was long-lived.

Throughout the late 1940s, Perutz also continued his work on glaciers in the Alps and helped found the Glacier Physics Committee in 1947. Though he had trouble recruiting able assistants who could also ski (the first two broke their legs), the work gave Perutz and his family the opportunity to spend summers in the mountains. Perutz’s research led him to conclude that glaciers flowed faster at the surface than at the bottom.

Perutz’s digestive attacks began increasing in intensity in the early 1950s to the point where, in 1954, he was hospitalized for ten days. While there, doctors looked for possible causes but came up empty and could only prescribe bismuth, with little effect. What did help, for reasons Perutz did not understand, was visiting the Alps, and so he arranged for a trip after being released from the hospital. Unfortunately the attacks resumed as soon as he returned to Cambridge, pushing Perutz to his limits – he considered resignation and even contemplated suicide. In desperate straits, he arranged for another trip to the Alps that spring but, once there, continued to get worse and, as an added complication, came down with scurvy.

When he returned, Perutz sought out other doctors who might be able to help, eventually visiting Werner Jacobson, who was also at Cambridge. Jacobson thought Perutz’s symptoms sounded like those of Celiac disease. He suggested that his patient stop eating wheat, or more specifically gluten, which immediately improved Perutz’s condition. Whenever the symptoms appeared again, as they did in the early 1960s, Perutz could trace them back to gluten; he eventually stopped eating any form of bread, since even gluten-free flour contained small amounts of gluten that negatively affected his health.

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Perutz in lecture. Image credit: Nature.

Perutz’s improved physical condition coincided with the final years of his triumphant work on a determination of the structure of hemoglobin. After working out a solution to interpret x-ray diffraction photos of proteins three-dimensionally, Perutz came upon the structure in September 1959, submitting his findings to Nature before heading to the Alps to ski over the winter break. By the time he returned, he was famous.  It was quickly and widely acknowledged that his work comprised a major breakthrough for both chemistry and biology.  As Hugh E. Huxley wrote, in 2002

He was the first person to find out how to determine protein structure by X-ray crystallography, after many years of patient struggle, and he applied the technique to solve the structure of haemoglobin, the oxygen-carrying protein in blood….The results showed that it was possible to see, in the atomic detail necessary to understand mechanisms, the structure of the macromolecules that carry out many of the functions of a living cell. Such knowledge is basic to the revolution that has swept through biology in the past 50 years, and to modern medicine and biotechnology.

By Fall 1962 there were rumors that Perutz would be awarded the Nobel Prize for chemistry. As October arrived, he began receiving calls from the press, but did not quite trust them. As the calls continued, Perutz received a telegram and thought, along with the rest of the lab, that it may be from the Nobel committee. Alas, the message was only from Nature asking how many reprints of his article Perutz wanted. That afternoon however, Perutz received another telegram, the one he had been waiting for. The lab celebrated with a champagne party as Perutz and Kendrew had been awarded the Nobel Prize for Chemistry, and Watson and Crick, along with Maurice Wilkins, would receive the Nobel Prize in Physiology and Medicine.

Perutz continued to work on the hemoglobin structure after his rise to fame, next turning to the question of how the structure changed with the uptake of oxygen. His Nobel lecture described this continued research on the four subunits within hemoglobin that changed their structure as oxygen was taken up; the first description of how proteins changed in structure.

In the years that followed, Perutz focused more on why this change occurred. Aided by automated x-ray diffraction machines and able assistants, Perutz’s lab was able to turn out more measurements than ever before. But the measurements, as Perutz later related, did not make any sense. After one of his research assistants completed his postdoc, Perutz looked closer at his results and realized that the new x-ray instruments had not been calibrated correctly.

In 1967, with all the bugs fixed, Perutz and his team put together the first atomic model of hemoglobin, but Perutz’s questions about why the structure changed still were not answered. By 1970, the lab was able to construct an oxygen-free model, allowing Perutz to compare it with the oxygenated model. As Perutz later described “there came this dramatic moment when between them, the models revealed the whole mechanism.” What he was able to see was how a slight movement of the iron atom triggered a change in the whole molecule. Thus, Perutz felt he was able to explain “all the physiological functions of hemoglobin on the basis of its structure.” The results were published in Nature.

Within the field, objections to Perutz’s explanation were numerous and he spent much of the next two decades refuting criticisms and refining his own explanation. At the same time, his celebrity also rose among scientists as he was increasingly invited to give lectures all over Europe and North America. By 1975 Perutz’s fame outside of scientific circles had grown such that Queen Elizabeth II invited him to visit with her at Buckingham Palace. Afterwards, Perutz expressed his regrets to the Queen’s secretary that “she had made me talk away like an excited little boy about my own doings and that I never asked her anything about hers.” Nonetheless, Perutz did hope that the Queen would enjoy his gift, the autobiography of Charlie Chaplin.

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Max Perutz with his hemoglobin model. Image credit: BBC.

By 1980 Perutz had begun to reach out to broader audiences more intentionally. Shortly after retiring from the chair of the Laboratory of Molecular Biology, Perutz wrote a memoir of his time there. This, in turn, inspired him to compile an account of his experiences during World War II and submit it to the New Yorker. Penned in 1980 but not published until 1985, “Enemy Alien” helped bring Perutz greater levels of fame, as he received more letters after its publication than he did congratulations for his Nobel Prize.

An Italian pharmaceutical company also approached Perutz in 1980 to give a lecture on the social implications of molecular biology. According to a 2001 interview, Perutz told the company that “molecular biology has no social implications,” but that he could talk about “science as a whole.” This spurred him to take more of an interest in broader scientific questions, ultimately leading him to adopt controversial stances combatting criticism of the Green Revolution, DDT use and nuclear power, among other issues in the headlines. It also evolved into an interest in philosophy – Karl Popper’s Open Society and its Enemies proved particularly impactful. By 1989, Perutz expanded his popular lectures into a book of essays, Is Science Necessary? which included writings that he had also done for the New York Review of Books as well as “Enemy Alien.”

While continuing to write for the New York Review of Books up to the end of his life, Perutz also pursued new research on proteins and hemoglobin, taking a particular interest in neurodegenerative diseases like Parkinson’s and Alzheimer’s. In 2001, right before he passed away, Perutz was still at the lab seven to eight hours a day (including lunch and tea), preparing a publication for the Proceedings of the National Academy of Sciences on the common structure of insoluble protein deposits in neurodegenerative diseases. He passed away at the age of 87, unable to reconcile his initial structure with x-ray diffraction photos which showed contradicting features that Perutz concluded arose from three different structures. The results were published in 2002, after Perutz had died, in two separate articles.

Max Perutz (1914-2002)

Max Perutz. Credit: Theresianische Akademie Wien.

[Ed Note: We mark the centenary of Max Perutz’ birth today with the first in a series of posts on his life and his associations with Linus Pauling. Today’s post focuses on his life from 1914-1941.]

Max Ferdinand Perutz was born May 19, 1914 in Vienna, the third child and second son of Hugo and Adele Perutz.  His birth came little more than a month before the assassination of Archduke Franz Ferdinand and the subsequent start of World War I. Vienna was largely untouched by the war, but suffered mightily from the economic depression that followed. The Perutzes, who had accumulated a substantial fortune from family textile concerns, lost their savings to the rapid postwar inflation. Nonetheless, according to biographer Georgina Ferry, the family managed to maintain an income and “within a few years of the war’s end, they were living as well as before.”

In a 2001 interview with Katherine Thompson for the British Library, Perutz said that he remembered little of these early years. He did recall being a “very delicate child,” contracting pneumonia three times before he was six and a very serious fever at age nine. Fortunately, he was able to recover from the fever after his nanny took him to a resort in the Alps for the winter. After World War II, chest x-rays revealed that Perutz had suffered from tuberculosis, the likely cause of his fever.

Perutz’s physical delicacy affected his social life as well; he described himself as a “weakling at school” who had no friends early on since he was sick so often. Because of his condition, Perutz did not excel at most sports. But his many holidays in the Alps led him to develop a lifelong love of rock climbing and skiing. These skills eventually earned Perutz the respect of his peers after he won a prize for the school skiing team.

Perutz attended private primary schools until entering the newly organized Realgymnasium, which brought a shift in focus from classics to modern languages and the sciences. Perutz described his early years of schooling as “eight years of unbearable boredom.” This boredom began to wane as Perutz gravitated toward English literature, an interest enabled by his Anglophile father who saw that he was tutored in English in addition to the more common French. Perutz secretly read Charles Dickens and other British novelists under the bench while at school, later furthering this passion with his first girlfriend, who was from England. Perutz’s parents expected him to take over the family textile business once he was old enough, and were heartened by his developing intellectual prowess.

However, the business route never appealed to Perutz, especially after he was exposed to chemistry by an influential teachers, and at eighteen he began formal pursuit of his interest in chemistry at the University of Vienna. (Protests from his parents were soothed by the help of a friend of Perutz’s older brother, a chemist at Dow.) As with his primary schooling, Perutz was not very impressed by the education that he received at university. He described the curriculum’s lack of mathematical training and decidedly practical emphasis as “chemistry done by heart” because of the reading and memorizing he was forced to do in lieu of actual laboratory work. But ultimately he made it through and, in the process, cultivated a new attraction to physics which he would later fulfill as a graduate student in England.

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Portrait of Perutz drawn by William Lawrence Bragg. Credit: MRC Laboratory of Molecular Biology

From Vienna, Perutz moved on to Cambridge, where he hoped to work with Frederick Gowland Hopkins, the university’s first chair of biochemistry and recipient of the 1929 Nobel Prize in Physiology for his work on the relation between vitamins and growth. Since Perutz showed up without letting anyone know, he did not find out that he could not work with Hopkins until he actually arrived. Chastened, Perutz looked elsewhere and ended up in the Cavendish Laboratory of Physics doing x-ray crystallography. “Without knowing it,” Perutz later recalled, this “was one of the best things I could have done.”  Supported by £500 sent by his father, Perutz settled in and was able to take care of his own finances for the duration of his doctoral studies.  His health continued to suffer though – once in England, he began to experience frequent and painful digestive problems.

The first project that interested Perutz was identifying radioactive deposits dug out from the cliffs in Cornwall. Perutz measured the half-life of the material, but found that it did not correspond to any known elements. Excited that he may have discovered a new element, Perutz shared his findings with Cambridge luminaries Ernest Rutherford and J. D. Bernal, who helped him to determine that the substance was, in fact, radium. Bernal also encouraged Perutz to publish his findings and to present them at a Royal Society soiree. This led to his first publication, “The Iron-Rhodonite from Slag,” which appeared in Mineralogy Magazine in 1937.

At the end of his first year at Cambridge, Perutz spent his summer holiday back in Austria and thought about what he might do for his doctoral dissertation. Felix Haurowitz, then at Charles University in Prague, suggested focusing on hemoglobin, telling Perutz that he could get crystallized hemoglobin from Gilbert Smithson Adair at Cambridge. When he returned and acquired the hemoglobin, Perutz says he “immediately got a lovely x-ray diffraction picture,” which “thrilled” Bernal.

In the midst of his hemoglobin research, Perutz also agreed to assist a man who came to the Cavendish Laboratory looking for researchers to satisfy his own interest in glacier development. Perutz saw this as a perfect opportunity to spend more time skiing in the Alps. He published his work in the Proceedings of the Royal Society in 1939, describing how melting and the movement of water contributed to glacier formation and flow.

In March 1940, Perutz wrapped up his Ph.D., which described the structure of hemoglobin and the x-ray methods used to develop the model. Yet the looming threat and subsequent reality of war overshadowed his findings and began to color components of his world that were much more important than his research.

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Credit: National Portrait Gallery, London.

As World War II approached, the Perutz family, still in Vienna, looked for ways to get out. The Perutzes were ethnic Jews, but Max’s parents were non-observant and Perutz himself had been baptized Catholic. As a young boy, Perutz was very devout, a character trait that he abandoned after his prayers that the Italians not invade Ethiopia were not answered. While his baptism was meant to protect him from anti-Semitism, he claimed that his family “very rarely” experienced discrimination before the Anschluss. Once the Nazis assumed power, the Perutz family quickly left with Max’s brother and sister going to the United States and his parents coming to stay in Cambridge. Hugo and Adele Perutz, used to supporting themselves, lost their businesses and spent all their money leaving Vienna – according to their son, they “were traumatized by suddenly being poor.”

To get them to England, Max both had to prove that he could support them and was also required to pay a thousand pounds, compelling him to sell some of his mother’s jewelry and to borrow funds to cover the rest. Around this time, William Lawrence Bragg, winner of the 1915 Nobel Prize in Physics, came to the Cavendish. Bragg was very excited about Perutz’s work with hemoglobin and helped him to secure a grant with the Rockefeller Foundation in New York. The grant provided £275 per year, enough for Perutz to prove that he could support his parents. But soon the family would come into even more trouble.

In May 1940, just two months after he finished his Ph.D., Perutz was interned by the British government. He was first taken and held in a school at Bury St. Edmunds, east of Cambridge, for one week before being transported to Liverpool. By July, Perutz, along with roughly twelve-hundred others, was shipped across the Atlantic to a camp near Quebec City, Canada, where the residents’ status was upgraded from “internee” to “civilian prisoner of war,” a change that promised access to clothing and army rations. In a 1985 essay for the New Yorker, titled “Enemy Alien,” Perutz wrote,

To have been arrested, interned, and deported as an enemy alien by the English, whom I had regarded as my friends, made me more bitter than to have lost freedom itself. Having first been rejected as a Jew by my native Austria, which I loved, I now found myself rejected as a German by my adopted country.

Perutz’s friends were working on his behalf to have him released, unknown to him since he could receive no communications.

Meanwhile, in Quebec, Perutz tried to make the best of things and organized a “camp university.” Hermann Bondi, a mathematician also from Vienna, taught on vector analysis, while Klaus Fuchs, a student at Bristol who fled Hitler’s persecution for being a communist, taught theoretical physics. For his part, Perutz drew on past research of his own, explaining the atomic structure of crystals to all who might be interested.

The Rockefeller Foundation did not forget about Perutz and arranged a professorship for him at the New School for Social Research in New York City. Hearing rumors that his father had also been interned and worried that he would not be able to obtain a visa to travel once he had been established in the United States, Perutz was eager to go back to England to check on his parents. After several delays and transfers, Perutz arrived back in Cambridge in January 1941, finding his father already released and his friends happy to see him.

Pauling and Proteins: The Beginnings of a Revolution

Linus Pauling and Robert Corey examining models of protein structure molecules, ca. 1951.

[Part 1 of 3]

An article with the somewhat cumbersome title “The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain” appeared in the April-May, 1951 edition of the Proceedings of the National Academy of Sciences. The article was written by Linus Pauling, Robert B. Corey and Herman R. Branson, working collaboratively at the Gates and Crellin Laboratories of Chemistry at the California Institute of Technology and communicated to PNAS on Pauling’s fiftieth birthday. The article is immediately notable in that it is first of seven written by Pauling and his collaborators on the nature of protein and published in that single issue of PNAS.

And as it turns out, these seven articles were revolutionary. While the very act of mailing in all seven at once was audacious, their contents solved riddles that many researchers “believed would not be solved for decades.” Max F. Perutz, a competitor of Pauling’s in the field of biochemistry, read all seven papers in one morning, after which he immediately raced to his lab. Utilizing Pauling’s predictions, he was able to conduct experiments that validated the hypotheses proposed by the papers. He wrote to Pauling that

The fulfillment of this prediction and, finally, the discovery of this reflection in hemoglobin has been the most thrilling discovery of my life.

“The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain” was presented as the lead article in the April-May 1951 PNAS. The main question asked by the paper was: What is the structure of polypeptide chains – the backbones of proteins? Pauling, Corey, and Branson claimed that the best way to determine the answer to this question was to acquire an “accurate determination of the crystal structure of amino acids, peptides, and other simple substances related to proteins.” By determining the attributes of these components, which acted as the building blocks of polypeptide chains, the researchers could then make reasonable estimations of what the finished product would look like. Pauling’s group was specifically searching for the interatomic distances between molecules, the bond angles of the chemical bonds, and “other configurational parameters” fundamental to the structures.

Pauling and his colleagues felt that their work answered these questions and that they had determined the parameters satisfactorily. They then used their data to determine that their basic shape was a hydrogen-bonded, helical configuration. They wrote that “An amino acid residue (other than glycine) has no symmetry elements…” (In biochemistry, “residue refers to a specific monomer,” which is “a molecule that may bind chemically to other molecules…”) Because the residues lacked symmetry elements which would force the polymer chain into a symmetrical pattern, “…the only [possible] configurations for a chain…are helical configurations.”

Figures from “The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain,” 1951.

Furthermore, the group determined that, based on their calculations of bond angles, there were five possible angles for the helical turns; 165°, 120°, 108°, 97.2°, or 70.1°. Of these, only two, 97.2° and 70.1°, were “reasonable” potential configurations for the polypeptide chain, based on observed interatomic distances. Hydrogen, carbon, oxygen and nitrogen are the elements that make up the polypeptide chain. The chemical bond between C-O and C-N are both double bonds (they have four electrons instead of two). These tight bonds, along with the measured interatomic distances of other components, indicated that the interatomic distances for the chain would have to be small, otherwise the chain would very quickly become unstable. This is the reason that only the 97.2° and 70.1° configurations were acceptable. The other three angles were unstable and would have unraveled because the N-H bonds had too much space between them. Whether the helix turned at a 97.2° or a 70.1° rotation depended on the number of residues per turn in the chain. Pauling and his associates proposed either a 3.7-residue helix or a 5.1-residue helix.

The article ended by explaining why competing hypotheses on the shape of polypeptide chains were incorrect. The article specifically pointed out three hypotheses authored by William Astbury and Florence Bell, William Lawrence Bragg, John Kendrew, and Max Perutz, and Maurice Huggins as being inferior. The Caltech group asserted that each of their models assumed a set number of residues in the polypeptide chains instead of potential variables, and only gave rough estimates of interatomic distances and bond angles. While they all agreed that a helix was the correct shape, the specifics of all other helix models were incorrect because of these deficiencies.

This first paper was just a piece of the larger argument that Pauling was making. Each article was in itself useful, but only when considering the larger sum of the full publication bloc could the full import and implications of Pauling’s work be made visible. Pauling’s thinking proved to be revolutionary and controversial, as such ideas often are. William Lawrence Bragg, a key competitor of Pauling’s, was especially critical. He felt numerous of the Caltech group’s ideas to be outright false, and even the most solid of Pauling’s assertions to be just baby-steps rather than major breakthroughs. Pauling, naturally, disagreed.

The Alpha Helix

Space-filling model of the alpha helix.

[The Paulings in England: Part 5 of 5]

It has been said that sometimes blessings come in disguise, and so it may be that we have the damp English spring to thank for the elucidation of the alpha-helix structure of alpha-keratin – a fundamental and ubiquitous secondary structure pattern found in many proteins.

Linus Pauling was plagued by sinusitis for much of his time in England, and for three days in March 1948 it had become severe enough to put him in bed (as he was fond of saying over the years, this was before his vitamin C days). After a day spent devouring mystery novels, Pauling asked Ava Helen if she would bring him some paper and his slide rule, at which point he started trying to figure out how polypeptide chains might fold up into a satisfactory protein structure.

Pauling’s canvas was just an ordinary 8 1/2 by 11 inch sheet of paper. His first step was to draw the correct bond angles and distances onto the sheet, as determined from previous x-ray crystallographic work on polypeptides. Next he folded the sheet along parallel lines into a sort of squared-off tube. Doing so allowed him to add in representations of hydrogen bonds, which the impromptu model suggested would form between amino acid residues and, as a result, hold the turns of the polypeptide together.

The model made sense and pretty quickly it was clear that Pauling had discovered something important.  As he later wrote, his folded creation “turned out to be the structure of hair and horn and fingernail, and also present in myoglobin and hemoglobin and other globular proteins, a structure called the alpha-helix .”

Reconstruction of the alpha-helix paper model. Drawn and folded by Linus Pauling, 1982.

Pauling kept this idea to himself until his return to the United States because something didn’t match up quite right with the current laboratory data. Specifically, the turns of Pauling’s helix didn’t mirror the 5.1 angstrom repeat found in all of William T. Astbury‘s x-ray patterns. Pauling’s structure came close, but made a turn every 5.4 angstroms, or every 3.7 amino acid residues.

After his return home, with the assistance of colleagues Robert Corey and Herman Branson, Pauling continued refining his alpha helix structure and developing others, including the beta sheet. Simultaneously, the Caltech group’s chief British rivals at the Cavendish Laboratory published a paper titled “Polypeptide Chain Configurations in Crystalline Proteins.” The paper promised more than it delivered though, and while it listed many possible structures, Pauling found none of them to be likely. The competition was still on.

Pauling was finally convinced to publish when he received word that a British chemical firm called Courtaulds had created a synthetic polypeptide chain that showed no sign of Astbury’s 5.1 angstrom reflection in x-ray diffraction images. This was enough evidence for Pauling to decide that the 5.1 angstrom repeat was, perhaps, not a vital component of all polypeptide chains.  And so it was that in April 1951 Pauling, Corey and Branson published “The structure of proteins: Two hydrogen-bonded helical configurations of the polypeptide chain,” in the Proceedings of the National Academy of Sciences.

After devouring the Pauling group’s results shortly after their publication, Max Perutz headed to the Cavendish lab at Cambridge to check the data himself. Having confirmed the structure in images of horsehair, porcupine quill, synthetic polypeptides, hemoglobin and, for good measure, some old protein films that had been tucked away, Perutz wrote to Pauling, “The fulfillment of this prediction and, finally, the discovery of this reflection in hemoglobin has been the most thrilling discovery of my life.” He then published an analysis of his own data, concluding, “The spacing at which this reflexion appears excludes all models except the 3.7 residue helix of Pauling, Corey and Branson, with which it is in complete accord.”

Video Link: Pauling Recounts His Discovery of the Alpha Helix

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It wasn’t until a year later that the mystery of Astbury’s 5.1 angstrom reflection was finally solved. In 1952, on a visit to the Cavendish, Pauling met Francis Crick, the then-graduate student who would go on to play a huge part in the discovery of the structure of DNA. The two maintained similar interests and during a taxi ride around Cambridge found themselves discussing the matter of the alpha helix. “Have you thought about the possibility,” Crick asked Pauling, “that alpha helixes are coiled around one another?” Whether Pauling had or had not considered this possibility remains a point of contention, but Pauling remembered replying that he had, because he had been considering a number of higher-level schemes for his helixes, including some which wound around each other.

Regardless, Pauling returned to Caltech and both he and Crick set to work on the problem. With help from Corey, Pauling discovered a means by which the alpha helixes could wrap around each other in a coiled-coil to produce the problematic 5.1 angstrom found in Astbury’s pictures of natural keratin.  Crick, in the meantime, was conducting a very similar study.  Pauling and Crick, independent of one another, ultimately submitted the solution to this puzzle for publication within days of each other, and at first there was a bit of grumbling as to whom the credit should be awarded. Though Crick’s note was published first, the Cavendish camp eventually conceded that Pauling’s paper included considerably more detail of consequence, and it was finally settled that both scientists had independently come to the same general conclusion.

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Pauling receiving his honorary degree from the University of Paris, 1948.

After Pauling’s two fruitful terms as Eastman Professor at Oxford were up in July, the family split their remaining time between travels in Amsterdam, Switzerland and Paris. Pauling rounded off the trip by receiving yet another honorary degree from the University of Paris, and on August 25, 1948, the Paulings set sail once more on the Queen Mary.

His eight months in Europe had been productive and enlightening, but Pauling was ready to return to Pasadena where he could share the myriad ideas he had generated and gathered during his time away from Caltech. As we have seen, he was especially eager to get back to work on proteins, writing shortly before his departure that “I have continued to work on my theory of metals, and have been doing nothing about proteins. However, I am looking forward to being back home, and to thinking about that subject again.”