Thermal Inactivation of Myosin A-Adenosine Triphosphatase in the Presence of F-Actin

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The influence of the concentration of F-actin on the inactivation of myosin A-ATPase in solution and in suspension has been studied. The reaction departs from typical first-order behavior in that the rate decreases as the reaction proceeds. The extent of this effect varied greatly with the amount of F-actin added and slightly with pH and ionic strength. The interpretation of the experimental results is discussed. A kinetic mechanism which qualitatively accounts for the observed behavior and which suggests the occurrence of two types of actornyosin complexes with respect to susceptibility to denaturation is proposed.
The rate of denaturation of myosin A has been found to decrease greatly on an addition of magnesium and also with a decrease in ionic strength at high (10.3) or low (6.0) pH values.