[Ca2+-activated ATPase reaction of myosin from human cardiac, skeletal and smooth muscle cells].

A comparative study of Ca2+ activated ATPase reaction of myosin isolated from cardiac, skeletal and smooth human muscles shows that on the molecules of all kinds of myosins there exist two types of centres binding the substrate CaATP with high and low affinity (Km approximately 1.6 x 10(-6) M and Km approximately 200 x 10(6) M respectively). Hydrolysis of ATP by myosin is noncompetitively activated by three types of Ca2+ binding sites on its molecule, having different affinity. The association constants (KaCa) for the smooth muscles are several times higher than those for skeletal and cardiac muscles.