Reappraisal of the binding of myosin subfragment 1 to regulated filaments in terms of the steric model of muscle relaxation

The sigmoidal form of the binding curves obtained [L. E. Greene and E. Eisenberg (1980) Proc. Nat. Acad. Sci. USA 77, 2616-2620] for the interaction of myosin subfragment 1 with regulated filaments is reinterpreted and shown to be consistent with a steric blocking model of muscle relaxation in which the interaction of tropomyosin with the myosin-binding sites on the actin filaments is considered to be an equilibrium process rather than an all-or-none phenomenon. Such an interpretation of the results has the advantage that dependence of the binding curve upon filament concentration is predicted, the previous models based on filament isomerization being deficient in this regard