Caldesmon: binding to actin and myosin and effects on elementary steps in the ATPase cycle

The actin binding protein caldesmon inhibits the actin-activation of myosin ATPase activity. The steps in the cycle of ATP hydrolysis that caldesmon c ould inhibit include: (1) the binding of myosin to actin, (2) the transitio n between any two actin-myosin states and (3) the distribution between inac tive and active states of actin. The analysis of these possibilities is com plicated because caldesmon binds to both myosin and actin and because each caldesmon molecule binds to several actin monomers. This paper reviews proc edures for analysing these interactions and summarizes current information on the stability and dynamics of the interaction of caldesmon with actin an d myosin. Possible effects of caldesmon on transitions within the ATPase cy cle of actomyosin are also discussed.