Abstract
An initial burst of Pi-liberation was observed not only from the myosin-ATP system but also from the cardiac myosin B-, the skeletal H-meromyosin-, and the skeletal subfragment S1-ATP systems. The amounts of the initial bursts from these systems were always almost one mole per mole of protein.
The time-course of ADP-liberation was followed by measuring the oxidation of NADH in the myosin-ATP system coupled with pyruvate kinase and lactate dehydrogenase. Liberation of ADP did not show an initial burst. The dependence of the rate of oxidation of NADH on the ATP concentration showed that myosin contains one mole of ATP-binding site per 4×105g. and in the steady state it contains no bound ADP.
The initial rapid liberation of Pi was not affected by DNP or G-strophanthin. The dependences of the reciprocals of the amounts of the initial bursts from the myosin-, and the H-meromyosin-ATP systems on various divalent cations were very similar to those of the rates of the O18-exchange reaction catalyzed by these two proteins, reported by Koshland et al.
