Croonian Lecture - On the structure of biological fibres and the problem of muscle

Abstract

On the basis of the slight variability of X-ray diffraction patterns in the extended beta-form, the folded chain alpha-form and the supercontracted form, keratin, myosin and fibrinogen form a related group distinct from, collagen, in which contraction results in complete disorientation with loss of diffraction arcs. Uncontracted muscle contains myosin in the alpha-form, which may be partially converted to the beta-form, or which on physiological or iodoacetate contraction assumes a form similar to supercontracted wool keratin. Length changes in muscle are not primarily micellar or fibrillar disorientation. Although entropy can account for the restoration of stretched rubber, H. J. Woods has shown that it makes a negligible contribution to the restoration of supercontracted wool and oriented myosin strip. Whewell and Woods have demonstrated a reversible 20-30% supercontraction of wool in cuprammonium solns. similar to normal muscle contraction, the upper limit of which corresponds to Ramsey''s limit for reversible contraction of muscle (delta state). Astbury proposes a structure for myosin in which portions of the protein chain which are capable of transverse folding occur in series with better crystalline aggregates which yield the relatively constant large-angle x-ray pattern.