Stimulatory effect of calponin on myosin ATPase activity

Calponin, a calmodulin-binding protein of smooth muscle that inhibits the actin-myosin interaction by binding to actin, was shown to bind to myosin and to stimulate the ATPase activity of myosin to some extent. Actin abolished this myosin-linked, stimulatory effect of calponin. Ca(2+)-calmodulin affected neither the myosin-binding activity nor the stimulatory effect of calponin. We further presented a few data which suggest that calponin may exert regulatory activity toward myosin in quite a different way from caldesmon, another smooth muscle protein that binds to myosin, actin, and calmodulin.