Kinetic studies with synthetic myosin minifilaments show the equivalence of actomyosin and acto-HMM ATPases.

The kinetic properties of actomyosin have been examined using complexes of actin with the recently described (Reisler, E., Smith, C., and Seegan, G. (1980) J. Mol. Biol., in press) short, bipolar synthetic myosin filaments (minifilaments). It is shown, in contrast to previous observations with aggregated and insoluble myosin, that the kinetic behavior of actomyosin is similar to that of acto-heavy meromyosin. Owing to their size, solubility, and stability under conditions of the actin-activated ATPase measurements, the minifilaments provide a well defined experimental system. Thus, they constitute a convenient and appropriate material for studying actomyosin interactions.