Elastic properties and α - β -transformation of fibrous proteins

Abstract

Our ideas on the amount of unfolding occurring during α-β-transformation are derived from the detailed studies by Astbury & Woods (1933) of the elastic pro­perties of wool and hair. Gaining an understanding of the phenomena of 'per­manent set' on the one hand and 'supercontraction' on the other, Astbury & Woods found the true reversible extension to be ca. 100%, and thus proposed that the β-chain is approximately twice as long as the α-chain. Some time later they studied myosin fibres in the same way, and Woods presented load/extension curves showing that though myosin fibres might be extended 120% there was a character­istic weakening at about 100% extension, and the maximum contraction (re­covery) of the most highly stretched fibres seemed to be about 50% (Astbury & Dickinson 1940). The measurement which could be related to the amount of chainfolding is the figure for the maximum reversible extension. At the highest exten­sions there is likely to be some 'drafting' or slipping, so that the figure we are interested in becomes the maximum contraction from the stretched length, i. e. the amount of recovery. As each member of the k. -m. -e. -f. group came to be studied by X-rays the elastic properties were also examined. Measurements given here for epidermin and fibrin are new, while those for myosin can be compared with previous results (Astbury & Dickinson 1940).