The mechanism of skeletal muscle myosin ATPase. The mechanism of ADP interaction.

The mechanism of interaction between ADP and the myosin active center has been studied using a transient kinetic technique. The results show that the interaction of ADP with the myosin active center is a homogeneous process independent of the association state of the active centers; namely, whether ADP interacts with the monomeric myosin subfragment-1, or with the dimeric forms heavy meromyosin and myosin. The kinetics of the interaction conforms to a simple two-step reaction mechanism for ADP binding. The kinetic and thermodynamic constants for this mechanism have been determined. In addition, analysis of the binding isotherm indicates that the two active sites in heavy meromyosin and myosin function as identical and independent sites.