[18O-exchange reactions in skeletal, cardiac and smooth muscle myosin].

18O-exchange reactions of skeletal, cardiac and smooth muscle myosin were studied. All investigated preparations of myosin catalyse two types of 18O-exchange--intermediate and direct exchanges in the presence of Mg2+. The dependence of 18O-exchange extent on divalent cations have appeared to be similar for different muscle types. This supports the hypothesis of similarity of ATP hydrolysis molecular mechanisms by myosin of different origin.