Unsteady rate of ATP hydrolysis by myosin and actomyosin in its initial phase.

Abstract

1. The time course of ATP hydrolysis by myosin, H-meromyosin, myosin B and synthetic actomyosin was followed. The rate of ATP hydrolysis in the initial phase was unsteady, and was grater than that of ATP hydrolysis in the steady state.2. This phenomenon was due to neither to the impurity in ATP sample, nor to the rapid liberation of orthophosphate bound to myosin by the addition of ATP.3. The time needed to get into the steady state was shortened by the addition of Mg++ and was elongated by the addition of Ca++, of pyrophosphate and of EDTA.4. The magnitude of Michaelis constant in the initial phase was different from that of Michaelis constant in the steady state.5. The cause of this phenomenon was discussed.