Myosin Ca (2 +) And Non-ca (2 +) Regulating Mechanism

Caldesmon is a calmodulin-binding protein, it consists of thin filaments of smooth muscle and is considered to be potential modulators of smooth muscle contraction and relaxation. It has been known that caldesmon can inhibit actin-activited myosin ATPase activity and this inhibition is reversed by Ca²⁺/calmodulin. In recent years, it has been found that caldesmon has direct regulation on myosin. Our recent study showed that trace amount of caldesmon could interact with myosin,when used in the concentration of 0.0001μM(10 thousands-fold lower than that of used in previous studies) in this assay the lowest CaD/myosin ratio was 1/10000,significantly increased the precipitations of 1μM unphosphorylated myosin, Ca²⁺-CaM dependently or independently phosphorylated myosin by MLCK. Trace amount of caldesmon could stimulated the MgATPase activities of these myosins but caldesmon could not impact on the function of phosphorylated myosin by PKA, this high efficiency of interaction between caldesmon and myosin maybe participate the regulation of myosin function.