THE BI-DIRECTIONAL REGULATION OF FILAMIN ON THE ATPase ACTIVITY OF SMOOTH MUSCLE MYOSIN

Objective. The dim of this study is to investigate the functional relationship between filamin, a known acfin bind-ing protein, and myosin and the effects of filamin on the interaction between myosin and aetin.Methods. Ultra-eentrifugafion method was used to investigate the binding of filamin to both phosphorylated and unphosphorylated myosins. Mg-ATPase activities of both phosphorylated and unphosphorylated myosim in the presence and absence of actin were measured to observe the effects resulted from filamin-acfin and filamin-myosin interactions. Results. It was found that filamin is also a myosin binding protein. Filamin inhibited the actin activated Mg-ATPase activity of phosphotylated myosin and stimulated Mg-ATPase of phosphorylated myosin in the absence of acfin; in addition, filamin stimulated Mg-ATPase activity of unphosphorylated myosin in both the presertce or absence of actin.Conclusion. The results suggest that the effects of filamin on the myosin Mg-ATPase activities are bi-directional, i.e., stimulatory via binding to myosin and inhibitory via binding to acfin.