A kinetic study of the K+ activated ATPase of myosin subfragment-1

The K+ activated ATPase activity of myosin subfragment-1 was measured under different conditions and enzyme kinetic parameters were calculated. The logarithm of Km varies linearly with ionic strength down to very low KCl concentrations, the logarithm of k2 vs. ionic strength, on the other hand, considerably deviates from linearity at low concentrations of KCl. ADP is a competitive inhibitor, like myosin ATPase, and with practically the same inhibitor constant. The energetical parameters of the decomposition (to products and enzyme) of the S-1--ATP complex are partically the same as those for myosin, the parameters of its formation, however, differ from the corresponding values for myosin: delta SI is considerably, delta HI significantly higher in the case of myosin. This may be the result of some kind of interaction of the two heads of myosin.