Intermediate states of actomyosin adenosine triphosphatase.

The early kinetic steps of actomyosin subfragment 1 (acto-S1) adenosine triphosphatase have been investigated by simultaneous monitoring of fluorescence and light scattering and also by observation of the time course of the production of phosphate. The results show that fluorescence enhancement occurs after the dissociation of actomyosin and that the rate of enhancement is similar to the maximum rate of enhancement for S1 alone, under similar conditions of pH and temperature. The maximum rate of the phosphate burst for acto S1 is also approximately the same as that for S1 alone. The maximum rates for fluorescence enhancement or phosphate formation are reached at much lower adenosine triphosphate concentrations for acto-S1 than for S1. An extension of the actomyosin scheme is presented which accounts for these results.