Linus Pauling: One day, when I was Eastman Professor at Oxford in the spring of 1948, I caught a
cold. It was before the vitamin C days! I caught a cold and after a day or two in
bed of reading science fiction and detective stories, I got tired of that, and thought,
why don't I discover the alpha helix? Something like that - why don't I try to find
how polypeptide chains are folded in a way compatible with all the knowledge we have
of structural chemistry and such that they can form hydrogen bonds to hold the parts
of the molecule together?
I took a piece of paper, much like this piece, and drew on it a representation of
an extended polypeptide chain, with the distances approximately right and the angles
right. Except, one angle did not have the right value. I still have that original
piece of paper, by the way. This is the bond angle of the alpha carbon that didn't
have the right value. I folded the paper - actually, it took several trials - I folded
it along several parallel lines through the successive alpha carbons.
Finally, I found a way by folding the paper to make this bond have an angle of 110
degrees. I finally found a way of folding such that when I fit it together, there
was an N-H-C-O bond formed by each N-H group, and each C=O group. The hydrogen bond
held the structure together and had just the right dimensions. I found that this structure,
which 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,
had 3.6 residues per turn of the helix. A helical structure where there are 3.6 residues
per turn.
