Activation energy myosin-actin interaction

In smooth muscle, myosin crossbridges have less myosin ATPase activity than those of skeletal muscle. As a result, the splitting of ATP that provides energy to "prime" the crossbridges, preparing them to interact with actin, is markedly reduced. Consequently, the rates of crossbridge cycling and tension development are slower. Furthermore, a slower rate of calcium removal causes the muscle to relax more slowly. 

Movement. Muscle contraction is accomplished by the interaction between two types of protein filaments, actin and myosin. Myosin also possesses an enzymatic activity for facilitating the conversion of the chemical energy of ATP into mechanical energy. 

Mechanical force is generated by the cyclic interaction of myosin heads with actin and the energy supplied from the hydrolysis of ATP (Fig. 5-33). Each myosin head can bind a single molecule of ATP. Myosin is an ATPase. The ATPasc activity is constitutive but can be increased up to 200-fold in the presence of actin. 

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