Inhibition of actomyosin subfragment 1 ATPase activity by analog peptides of the actin-binding site around the Cys(SH1) of myosin heavy chain

The synthetic heptapeptide, Ile-Arg-Ile-Cys-Arg-Lsy-Gly-ethoxy, an analog of one of the actin binding sites on myosin head (S-site) (Suzuki, R., Nishi, N., Tokura, S., and Morita, F. (1987) J. Biol. Chem. 262, 11410-11412) was found to completely inhibit the acto-S-1 (myosin subfragment 1) ATPase activity. The effect of the heptapeptide on the binding ability of S-1 for F-actin was determined by an ultracentrifugal separation. Results indicated that the heptapeptide scarcely dissociated the acto-S-1 complex during the ATPase reaction. Consistent results were obtained from the acto-S-1 ATPase activities determined as a function of S-1 concentrations in the absence or presence of the heptapeptide at a fixed F-actin concentration. The heptapeptide reduced the maximum acto-S-1 ATPase activity without affecting the apparent dissociation constant of the acto-S-1 complex. The heptapeptide bound by a site on actin complementary to the S-site probably inhibits the activation of S-1 ATPase by F-actin. These results suggest that S-1 ATPase is necessary to rebind transiently with F-actin at the S-site in order to be activated by F-actin. This is consistent with the activation mechanism proposed assuming the two actin-binding sites on S-1 ATPase (Katoh, T., and Morita F. (1984) J. Biochem. (Tokyo) 96, 1223-1230).