Force of Nature- The Life of Linus Pauling

by Thomas Hager

  The payoff was to be substantial: not just the structure of proteins and the molecular mechanism of biochemical reactions, but the birth of a new era in biology. "We believe that the science of biology is just entering into a period of great and fundamental progress, similar to that through which physics and chemistry have passed during the last thirty-five years," Pauling wrote.

  Pauling then turned to costs. He figured they would need two new buildings, construction funds for which could probably be raised among Caltech trustees, with equipment, staffing, and long-term support coming from the Rockefeller Foundation. He estimated that the total cost of staff, equipment, and maintenance would come to $400,000 per year for fifteen years, for a total of $6 million.

  It was the single largest grant request Caltech had ever made. It was the largest request Weaver had ever seen.

  When an apprehensive Beadle visited Weaver a week after the grant proposal arrived, he was relieved. "I didn't have to give him a sales talk. I've never seen a fellow so enthusiastic about a place as he is about Caltech." The $6 million price tag, Beadle wrote Pauling, looked "pretty big to him." But overall, Weaver considered it "a magnificent plan." Weaver pledged that he would try it out on his board but warned the Caltech duo that it would certainly take quite a while to sell an idea this expansive. While they waited, Beadle and Pauling knocked on the doors of other granting agencies. Soon money began flowing in for the grand plan: $300,000 over five years from the National Foundation for Infantile Paralysis, smaller sums from the Public Health Service and a number of other groups.

  Despite Weaver's enthusiasm, the Rockefeller Foundation hesitated. While board members debated the merits of the proposal, Weaver pried loose a significant amount of interim funding, fifty thousand dollars per year, for 1946 and 1947. Between that and the other grants—which now included a wide-ranging miscellany of money from government, industry, and foundations, including some grants devoted to finding cures for cancer—Beadle and Pauling had enough to get started in style. By 1947, the chemistry division's budget was double that of just six years earlier, and the biology division's was nearly triple.

  For two long years, the Rockefeller Foundation's board wrangled over funding the larger proposal. The delay was rooted in an internal debate over the foundation's role in postwar science. The climate for the funding of science had changed rapidly thanks to the government's infusion of vast sums of money for wartime projects. It seemed certain that large-scale government support for basic science would continue in some form, taking away much of the perceived need for the foundation to fund projects as big as Pauling's. The social aims of the board had changed, too, since the Depression-era Science of Man days. The board was shifting its emphasis in response to a new set of perceived needs, away from basic science and toward agricultural and social-science research—especially projects related to developing nations, which were seen as seedbeds for democracy and battlefronts between capitalism and communism during the coming decades.

  In that context, regardless of its merits, a basic science program on the scale of Pauling's had a slim chance of getting funded by the Foundation. As the board continued to deliberate, the numbers got smaller and smaller, until finally, in 1948, the group made its final decision: $100,000 per year for seven years.

  It was a fraction of Pauling's $6 million dream, but it was still one of the largest single grants ever made to Caltech—and the biggest the Rockefeller Foundation gave to any postwar basic science program. It was enough to pay for substantial expansion of Pauling's programs for an extended period of time, and it would make his chemistry group one of the best funded in the nation. Fueled by that money and the other private funds Pauling and Beadle were obtaining, guided by their closely cooperative leadership and staffed by a group of outstanding younger scientists, Caltech would become during the next decade America's nursery—and one of the most important site in the world—for the development of the infant field of molecular biology.

  What made it possible? "The answer can be found in just two words," said Warren Weaver: "Beadle and Pauling. These were two nucleating centers around which ideas developed and between which ideas resonated. It is just exactly as though there were all sorts of shared electrons in the system revolving around these two great centers, with a frequency of interchange for which I hardly know a parallel anywhere else."

  Grape Jelly and Hogwash

  The analogy of a chemical bond between the two men was not quite right, however. Beadle and Pauling got along well and instituted a close advisory relationship between chemistry and biology at Caltech; the two divisions would attend each other's seminars and scientists would occasionally cross the disciplinary fence to help with each other's research or provide advice. But the appearance of a united front was more for funding purposes than a reflection of joint research. After the Rockefeller money was in hand, Pauling and Beadle followed generally independent lines of research. Rather then resonance, their relationship was better described by a word that became Pauling's leitmotiv during the years immediately following the war: complementarity.

  Complementarity was a concept that grew directly out of his immunological work. Pauling's explanation of the binding between antibody and antigen as a matter of precise molecular fit, a complementary, hand-in-glove fit that brought the atoms on both surfaces into contact close enough to allow the formation of a number of weak van der Waals bonds, offered a way to explain other biological phenomena. Life at the molecular level, Pauling began to realize, was largely a matter of specificity, of molecules in the body being able to recognize and bind only to certain target molecules and ignore all the rest. Antibodies had to recognize and bind to specific antigens, enzymes to specific substrates, genes, in some mysterious manner, both to each other and their specific protein products. The mechanism of this exquisite biological specificity was unknown. But Pauling thought that his approach, based on precisely complementary shapes, was the key.

  The major lesson from his antibody research, he was beginning to understand, was the way it illuminated the relationship between molecular structure and biological specificity. Before his death in 1943, Landsteiner had asked Pauling to write a chapter on the chemical basis of specificity for a new edition of his immunology book. Pauling's chapter, which he called "Molecular Structure and Intermolecular Forces," was a concise primer summarizing his understanding of the ways that protein molecules could recognize and attach to specific targets. In these systems, he emphasized, shape was everything, precisely complementary coin-and-die shapes that fit together and were bound through the aggregate action of weak bonds. Chemistry, as most chemists understood it—the specific reaction of molecules to form strong covalent or ionic bonds—had little to do with it.

  When published in 1945, Pauling's chapter became not only the first review to explain clearly the relationship between modern structural chemistry and immunology, but also the first to show compellingly that most, perhaps all, biological phenomena at the molecular level could be adequately explained through the imaginative application of accepted chemical principles. Because it was published in an immunology text, it had relatively little impact on chemists. But it had a seminal influence on some of the young postwar biologists and immunologists who read it. Future Nobel Prize-winning immunologist Joshua Lederberg, for instance, thought it was one of the most important things Pauling ever wrote, a guidebook for fledgling molecular biologists hoping to understand a plethora of confusing questions.

  The idea that immunological specificity was due to the ability to assume precise complementary molecular shapes fit both with what Pauling and Delbruck had proposed on a theoretical basis in their 1940 paper and with Pauling and Mirsky's concept of proteins as chain molecules held in precise shapes by hydrogen bonds. But the idea went far beyond immunology.

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  In 1944, the father of wave mechanics, Erwin Schroedinger, then living in Dublin, published a small book called What Is Life? Because of the fame of its author, it immediatel
y received wide attention. It was an odd book, a somewhat poetic attempt to apply Schroedinger's creative imagination to the big questions of biology, and it was filled with what Pauling saw as woolly theorizing. In it, Schroedinger addressed an old paradox: How, in a universe that tends toward maximum entropy, could fantastically organized living systems both exist and re-create themselves? The old laws of physics, he argued, could not account for life. He proposed instead a new concept called "negative entropy." By somehow feeding upon this undiscovered substance, living organisms could counter the pull of dissolution. Within this theoretical framework, he proposed that the gene took the form of a self-replicating "aperiodic crystal." Vague as it was, Schroedinger's book exerted a powerful influence upon young postwar physicists, many of whom became attracted to biology because of it and devoted themselves to the search for the new laws of physics waiting to be discovered in the cytoplasm of living cells.

  Pauling thought the book was hogwash. No one had ever demonstrated the existence of anything like "negative entropy," and the gene was most likely a protein chain, a structure that appeared to be stable enough to exist in the body in a number of forms, not whatever an "aperiodic crystal" was supposed to be. "Schroedinger's discussion of thermodynamics is vague and superficial to an extent that should not be tolerated even in a popular lecture," he said. "It was, and still is, my opinion that Schroedinger made no contribution to our understanding of life."

  Pauling had his own, less exotic ideas about the nature of life. "Schroedinger says that living matter may be expected to work in a manner that cannot be reduced to the ordinary laws of physics, and that the interplay of atoms in an organism differs from the interplay in non-living matter," Pauling wrote a friend. "I do not think that such a difference will in fact be found." Life, in Pauling's view, could be reduced to "the possession of specific characteristics and the ability to produce progeny to which these specific characteristics are passed on." It was a matter of molecular specificity, and it could be adequately explained by the principles of chemistry.

  While Schroedinger dreamed of streams of negative entropy, Pauling found inspiration in grape jelly. He saw his theme of molecular complementarity played out in his kitchen, on the sides of a jam-jar left out by his children. There appeared after a few days, at the edges of the sugary goo, a sprinkling of small crystals of potassium hydrogen tartrate (cream of tartar), a common constituent of grape juice. And here was the crux of the mystery: How did the molecules of cream of tartar separate themselves from the thousands of molecules present in the jelly, aggregate only with each other, and arrange themselves into highly organized, molecularly pure crystalline lattices? Of course, Pauling saw, it worked because of complementary structure. Any small aggregate of the chemical would act as a seed. On the surface of the seed crystal would be holes to fill, spaces for new molecules. But only a molecule of the right size and shape would fit properly. Because the holes were made by potassium hydrogen tartrate molecules aligning themselves, they would fit more of the same. Anything else would be too big or too ill-shaped to create the proper weak forces for binding, or so small it would float in and out; anything else would be less stable and therefore less likely to last for any period of time. Thermodynamics favored the most compact structure, the pure crystal, over a more random arrangement. Perfect crystals could arise out of grape jelly without the aid of new laws of nature. This was the way that crystals formed in the ground, in caves, in the sea, under conditions far less unusual than a living body. In the high temperatures and odd chemical environment of a living body, why shouldn't even more unusual reactions take place?

  "We are so far from equilibrium that even highly improbable reactions can occur, without violation of the laws of thermodynamics. Many of these highly improbable reactions depend upon having a seed, a template that directs the reaction. Examples are known in inanimate nature. The responsible mechanism is the same as in living organisms," Pauling believed, "detailed molecular complementariness."

  Schroedinger was wrong; no new laws were needed. Pauling was seeing now a great new piece falling into place, an extension of his worldview from inorganic crystallography to all of biology. What was true for minerals was true for animals. And vegetables, too. The known natural laws, the same unifying ideas from chemistry informed by modern physics, bound the universe. "We may say that life has borrowed from inanimate processes the same basic mechanism used in producing these striking structures that are crystals," Pauling said. This chemical continuum that ranging from molecules to man was beautiful and soul satisfying. He was sure he was on the right track. He could feel that he was right.

  After 1945, molecular biology became as important and involving to Pauling as crystal structure or the chemical bond had been, and he brought to his new passion the same brilliance and dash that served him so well in other fields. He threw himself into it, expanding his journal reading to include biochemistry, physiology, genetics, enzymology, and a bit of bacteriology and virology, looking for soft spots, areas of least resistance where he might be able to employ his ideas about structural chemistry to answer biological questions.

  Enzymes were an early target. Many important biochemical reactions seemed to proceed in unlikely environments or at rates faster than simple chemistry could explain. The agents responsible were thought to be enzymes, a family of protein molecules that acted as biological catalysts, speeding reactions without themselves being changed.

  Most chemical reactions proceeded something like a train going over a hill, with a specific amount of energy—activation energy—required to boost the starting reactants to the top, where they were energized enough to combine or split apart or whatever they were going to do; the products would then fall down the other side of the energy curve to a new stable state. Catalysts appeared to work by somehow lowering the hill, reducing the activation energy needed to get a reaction going. The lower the hill, the faster the reaction could take place. It worked both ways, of course; a lower hill also made it easier for products of the reaction to re-form the original reactants. The overall effect depended on relative concentrations: If there were more reactants around than products, the catalyst would tend to push the reaction in one direction, pumping out more product until the concentrations were equalized. In the body, enzymatic reactions were kept moving in the right direction by burning up or otherwise using the product.

  Enzymes were also highly specific, each one working its magic only on one set of reactants and products. The digestive enzyme trypsin, for example, catalyzed the chopping of protein chains into smaller pieces. But its point of action along the chain was precise; it worked only at the spot where two particular amino acids were linked together and at no other location. To Pauling, this specificity was easy to understand: Enzymes, like antibodies, would be shaped to fit their targets; they would have a complementary structure. But complementary to what? The necessary clue was that an enzyme worked both ways, reactant to product and product back to reactant. "The fact that it had to speed up both the forward and back reaction indicated to me that the structure that the enzyme is complementary to had to be midway between the reactants and the products," Pauling said. This correlated to a hypothetical structure enzymologists called the "activated complex," a form midway between reactant and product that would exist for only a fraction of a second during an enzymatic reaction. Then, Pauling said, "it was obvious—to me at any rate—what the answer was to why an enzyme is able to speed up a chemical reaction by as much as 10 million times. It had to do this by lowering the energy of activation— the energy of forming the activated complex. It could do this by forming strong bonds with the activated complex, but only weak bonds with the reactants or products." In Pauling's view the enzyme's binding site was a close enough fit to a target molecule to loosely grab hold of it but fit it tightly only when the target was eased into a bent or strained position. The enzyme acted somewhat like a set of molecular pliers, bending the target molecule and making it easier to break it into pieces. Once
broken, the resulting products, too, would have a shape only partially complementary to the enzyme binding site, loosening the fit and making it easier to float away from the enzyme. There was no reason that the same process, Pauling saw, could not work in reverse, with the enzyme binding the products loosely, bringing them close together and easing the back-reaction to the original target. It all worked through complementary shapes.