Characterization and ATPase activity of human platelet actomyosin

Platelet actomyosin, partially purified by successive precipitation had a specific viscosity of 0,15 and a sensitivity to ATP of 60 %. The enzyme preparation was separated into the actin and myosin components and some myosin fragments by SDS-polyacrylamide gel electrophoresis. The ATPase activity of platelet actomyosin showed pH optima at pH 5.8 and pH 9.5. The influence of the concentrations of calcium and ATP on the ATPase activity was studied and evidence was obtained that Ca-ATP was the substrate. Non-competitive inhibition was brought about by free ATP. Competitive inhibition was observed in the presence of ADP