[Study of the stationary kinetics of the myosin ATPase reaction in the presence of calcium].

Calcium activation of myosine ATPase is investigated. Dependency of the hydrolysis rate on total concentration of metal ions and substrate and kinetics of the reaction under [ATP]tot. equals [Ca]tot. are studied. Dependency of upsilon on [Ca]tot, was found to be complex under comparable concentrations of ATP and calcium at the range of 0.1-1 mM. The data obtained show that the complex character of myosine ATPase reaction in the presence of calcium is due to a dual nature of the enzyme activation with calcium ions: CA+2-induced transition of myosine from low-active into active form and the formation of new easily hydrolyzible substrate (Ca ATP). Low-active form of the enzyme is a protein which is tightly bound with magnesium while active myosine is free of bivalent cations or is weakly bound with calcium. This two enzyme forms are indistinguishable kinetically. It is shown that Ca+2 at high concentrations is capable to substitute magnesium ions bound to the protein molecule. Activating effect of free metal on myosine ATPase is found to come to the protection of the enzyme from magnesium inhibition.