[18 O-exchange reactions catalyzed by myosin of calf intestine smooth muscle].

18O-exchange reactions of smooth muscle myosin of calf intestine were studied. Smooth muscle myosin, similar to skeletal myosin, catalyses two types of 18O-exchange reactions--intermediate and direct. Only quantitative differences of the exchange intensity are observed. 18O-exchange dependence on bivalent cation and nucleotide nature is found. The comparison of 18O-exchange characteristics for myosins of smooth and skeletal muscles confirms the hypothesis on the similarity of molecular mechanisms of ATP hydrolysis by myosin from different muscle types.