As Corey and Pauling refined their structures, word reached Pasadena that Courtaulds,
a British chemical firm working on synthetic fibers, had come up with some interesting
data. Researchers there had discovered a way to make synthetic polypeptide chains
by stringing together a single type of amino acid (instead of the mix of amino acids
found, for instance, in natural keratin). Pauling was especially interested in the
fact that these pure Courtaulds chains, when x-rayed, showed no signs of the confounding
5.1 angstrom repeat that Astbury had found in all natural keratins.
What did that mean? To Pauling, it strengthened the case that Astbury's 5.1 angstrom
reflection was not, after all, an absolute requirement for all polypeptide chains.
If it was not an absolute requirement, there was at least some support for he and
Corey ignoring it. The Courtaulds synthetic fibers also appeared to be long-chain
molecules that assumed a pencil-like shape (which could be explained by their being
helixes), that were hydrogen-bonded along their length (as Pauling's models predicted).
His belief in helixes strengthened, Pauling continued to expand his model-building,
coming up with additional theoretical protein structures, and working with Corey to
construct large-scale, space-filling versions of their helixes. The news began to
circulate at Caltech that Pauling was onto something big. When he announced that he
was going to give a seminar on protein structures he drew a large crowd of colleagues
and students. "Everybody knew this was going to be pretty hot stuff," remembered one
biology professor.
Pauling made a show of it, entering the large lecture room flanked by assistants carrying
a variety of props. One particularly interesting piece looked like a tall sculpture
wrapped in cloth bound with a string. Pauling started his talk by describing the basics
of protein structure, drawing illustrations of flat peptide bonds and hydrogen bonds
on a chalkboard. He held up a child's set of soft plastic pop-beads and snapped them
together to show how amino acids could connect end-to-end. Still talking, he pulled
a small jackknife from his pocket, opened it, and approached the wrapped sculpture,
which everyone now realized was his finished model of a basic protein structure. Pauling
seemed ready to reveal it, but then he backed off, continuing his talk, building suspense
- a trick he pulled several times. Finally he cut the cord and revealed his masterpiece:
A skein of red, white, and black atoms twisted into a thick, knurled column. It was
the alpha helix. And it was stunning. Pauling and Corey had fashioned it not from
the old ball-and-stick models that looked something like Tinker Toys, but in a new
form that they helped design, a so-called space-filling model in which the atoms,
each colored according to its element, fitted tightly next to each other. The result
was a solid-looking structure in which the helix's essentials could be more easily
grasped, almost felt, its length, depth, density, curve, and atomic relations clearly
apparent.
It was a triumphant unveiling. Pauling ended his talk with evidence that his helical
structures might exist in a variety of natural proteins. Afterward he was surrounded
by admirers. The show was a sensation.
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