The interaction of myosin with adenosine triphosphate

Abstract

1. 1. A light-scattering study has been made of the interaction of adenosine triphosphate (ATP) with myosin, using for the analysis the extrapolation method of B.H. Zimm. Certain ultracentrifugal observations supplemented the study. 2. 2. Addition of ATP to dilute solutions of either 5- or 24-hr, rabbit myosin extracts (pH 7, 0.6 M KCl, 0.001 M Ca ++) causes a reversible shape change at constant molecular weight, indicating no depolymerization into “actin” and “myosin-A.” 3. 3. At all times during the interaction with ATP, the myosin particles appear to be roughly cylindrical. Addition of ATP causes an extension of these cylinders, followed by a contraction after sufficient ATP is enzymatically hydrolyzed. Shape at any instant appears to be strictly determined by ATP concentration; the velocity constant of dephosphorylation can be obtained from light-scattering data alone, as well as from phosphate measurement. 4. 4. Between the fifth and twenty-fourth hour of extraction, the myosin particles are progressively aggregated. This aggregation is not due to the progressive addition, in substantial quantities, of a non-ATPase component. 5. 5. In the light of present evidence, the interaction of ATP and myosin can be plausibly explained by adopting an “entropic-electrostatic” model of the myosin particle.