Effects of various concentrations of MgATP on the superprecipitation and ATPase activity of scallop striated muscle myosin B1.

1. The superprecipitation and ATPase activity of scallop striated muscle myosin B showed essentially the same biphasic pattern as that of vertebrate skeletal muscle myosin B in its responses to changes in the MgATP concentration. Ca2+ had no effect at MgATP concentrations less than 10(-5) M. 2. The superprecipitation of gizzard myosin B showed a weak biphasic pattern, but its ATPase activity showed no sign of a biphasic pattern up to 3 x10(-3) M MgATP, in accord with the result of Bremel (1974). 3. Thus scallop striated muscle is classified into the same group as vertebrate skeletal muscle as far as its response to changes in MgATP concentration is concerned. Gizzard is distinct from the other two kinds of muscle.