Allosteric regulation of platelet actomyosin

The kinetic properties of platelet actomyosin have been examined to understand the mode of hydrolysis of its substrate ATP. In the presence of divalent cations, ATP hydrolysis deviated from Michaelis-Menten kinetics in such a way as to indicate cooperative effects, with a sigmoidal velocity $\text{vs.}$ substrate curve and a Hill slope of 2.4. In the absence of added divalent cations, linear Michaelis-Menten kinetics were obtained and the Hill slope reduced to 1.0. These results indicate an allosteric regulatory site on platelet actomyosin.