Effect of Calponin on Actin-Activated Myosin ATPase Activity

Abstract

Calponin inhibited the actin-activated myosin MgATPase activity in a dose-dependent manner without affecting the phosphorylation level of myosin light chain. This inhibition was Ca²⁺-independent. The decrease in enzymatic activity of myosin was correlated with binding of calponin to actin-tropomyosin filaments. Caldesmon showed a further inhibition of the calponin-induced inhibition of MgATPase activity of the thiophosphorylated myosin. Calponin-induced inhibition of the myosin MgATPase activity was reversed by the addition of calmodulin only in the presence of Ca²⁺. These results suggest that calponin acts as an inhibitory component of smooth muscle thin filaments.