Myosin cross-bridge cycling, rates

It simulates the activity of myosin ATPase, which results in contraction of the muscle (i.e. increased cross-bridge cycling). This increases the rate of utilisation of ATP and hence increases the concentration of ADP. 

Myosin, which increases the rate of the cross-bridge cycling. 

Haeberle JR (1994) Calponin decreases the rate of cross-bridge cycling and increases maximum force production by smooth muscle myosin in an in vitro motility assay. J Biol Chem 269 12424-12431... 

When smooth muscle myosin is bound to F-actin in the absence of other muscle proteins such as tropomyosin, there is no detectable ATPase activity. This absence of activity is quite unlike the situation described for striated muscle myosin and F-actin, which has abundant ATPase activity. Smooth muscle myosin contains fight chains that prevent the binding of the myosin head to F-actin they must be phosphorylated before they allow F-actin to activate myosin ATPase. The ATPase activity then attained hydrolyzes ATP about tenfold more slowly than the corresponding activity in skeletal muscle. The phosphate on the myosin fight chains may form a chelate with the Ca bound to the tropomyosin-TpC-actin complex, leading to an increased rate of formation of cross-bridges between the myosin heads and actin. The phosphorylation of fight chains initiates the attachment-detachment contraction cycle of smooth muscle. 

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