The Special Feature of Calponin on Myosins Phosphorylated by MLCK and PKA Respectively

Objective: To reveal the special feature of calponin (CaP) on myosins of different states. Methods: Myosin phosphorylation determination, myosin Mg2 +-ATPase measurement and protein binding assay were used in this study. The lowest CaP/myosin ratio used in the assay was 1/10000(mol/mol), which was 10 thousands-fold lower than the CaP/myosin ratio used in previous studies. Results: In the absence of actin, micro-amount of calponin (MAC) stimulated the Mg2+-ATPase activities of myosin in different states slightly but significantly; and more importantly, MAC significantly increased the precipitations of unphosphorylated myosin, Ca2 + -de-pendently and independently phosphorylated myosins by MLCK but not the myosin phosphorylated by PKA. Conclusion: MAC has a high efficient and selective effect on myosin in the absence of actin.