Actomyosin adenosine triphosphatase regulation by intramolecular myosin mechanisms. Myosin light chains functions and rod modification effects.

Mechanisms of the actomyosin ATPase modulation via the myosin light chains (LC) in various myosin types are discussed. The essential LC increase the stability of the myosin heavy chains (HC) in the myosin heads and, under certain conditions, they can affect the degree of interaction of HC with actin. The regulatory LC (RLC) are sensitive to calcium binding on specific sites or to calcium activated phosphorylation. These factors induce changes of the RLC state followed by changes of the HC state in response to calcium concentration changes during the contractile process. Direct calcium binding or phosphorylation effects in various muscles are mediated by special types of RLC and HC. Several examples of actomyosin ATPase changes induced by modifications of the myosin rod are compared. A common feature of these effects is a possible involvement of certain configurational changes of the myosin molecule. These changes can affect the spatial position of the myosin heads and the myosin-actin interaction.