X-Ray Evidence for a Conformational Change in the Actin-containing Filaments of Vertebrate Striated Muscle

Abstract

The control of vertebrate striated muscle from rest to activity is regulated by the combination of the regulatory proteins tropomyosin and troponin on the thin actin filament (see reviews by Ebashi and Endo, 1968; Ebashi et al., 1969). In the absence of calcium the regulatory proteins inhibit the actin-myosin interaction. Activation of muscle is caused by calcium binding to troponin which then removes the inhibition. Since there is only one troponin molecule for every seven actin molecules (Weber and Bremel, 1971) and troponin does not interact with actin, then the control of activation is presumably mediated by the tropomyosin molecules which run along the grooves in the actin filaments (Hanson and Lowy, 1963; Moore et al., 1971). It is, therefore, of importance to investigate any structural changes that occur in the thin filaments when actin-myosin interaction is allowed to take place, for such changes may give us information about the...