The inconsistency between the 5.4 and 5.1 Å continued to worry me until one morning about two years later when Francis Crick arrived at the lab with two rubber tubes around which he had pinned corks with a helical repeat of 3.6 corks per turn and a pitch of 5.4 centimeters.
He showed me that the two tubes could be wound around each other to make a double helix such that the corks neatly interlocked. Perutz works at the Medical Research Council's Laboratory of Molecular Biology, Cambridge CB2 2QHQ, UK, with support from the U.
When the structure of hemoglobin was finally solved, the hemes were found to lie in isolated pockets on the surface of the subunits.
Without contact between them how could one of them sense whether the others had combined with oxygen?
Kendrew and I had great difficulty in building real models of helical polypeptide chains with the right pitch; no matter whether we built them with two, three or four amino acid residues per turn, their bond angles were always strained. In their first paper they proposed an answer to the longstanding riddle of the structure of a-keratin, suggesting that it consisted of helical polypeptide chains with a non-integral repeat of 3.6 amino acid residues per turn. Elliott and their colleagues at the Courtaulds Research Laboratories. In contrast to Kendrew's and my helices, theirs was free of strain; all the amide groups were planar and every carboxyl group formed a perfect hydrogen bond with an imino group four residues further along the chain. In mad excitement, I cycled back to the lab and looked for a horse hair that I had kept tucked away in a drawer.
After some months we published our work jointly with Bragg in the found a series of papers by Linus Pauling, the famous American chemist, together with the crystallographer R. Their helix had a pitch not of 5.1 Å, as Astbury's X-ray picture seemed to demand, but of 5.4 Å, which was consistent with the repeat found in fibers of certain synthetic polypeptides by C. I stuck it on a goniometer head at an angle of 31° to the incident X-ray beam; instead of Astbury's flat plate camera I put a cylindrical film around it that would catch all reflection with Bragg angles of up to 85°.
As soon as I put the light on I found a strong reflection at 1.5 Å spacing, exactly as demanded by Pauling and Corey's a-helix.
The reflection did not by itself prove anything, but it excluded all alternative models that had been put for-ward by ourselves and others and was consistent only with the a-helix.
By temperament, perhaps, I experimented, whereas Jacques Monod thought.
True science thrives best in glass houses where everyone can look in.