Bill Astbury, a physicist and X-ray crystallographer working for the Wool Research Association in Leeds (United Kingdom), discovered that the fibrous protein keratin, found in wool, horn, nails and muscle, gave a common X-ray diffraction pattern consisting of just two reflections, a meridionalone at 5.1 Å and an equatorial one at 9.8 Å.
Astbury called this the a-keratin pattern. When these fibers were stretched under steam, a new pattern appeared with a meridional reflection at 3.4 Å and two equatorial ones at 4.5 and 9.7 Å. Astbury called this the b-keratin pattern. He concluded that it arose from the regular repeat of amino acid residues along straight polypeptide chains, whereas the chains in a-keratin must be folded or coiled such that several amino acid residues form a pattern repeating every 5.1 Å along the fiber axis.
It appeared that the key to understanding the structure of proteins lay in the ...
