Control of actomyosin interactions in smooth muscle and nonmuscle cells (could act as a bridge between myosin and actin filaments). Inhibits the actin-activated ATPase of myosin this inhibition is attenuated by calcium-calmodulin and is potentiated by tropomyosin. Interacts with actin, myosin, 2 molecules of tropomyosin and with calmodulin. On thin filaments in smooth muscle and on stress fibers in fibroblasts (nonmuscle).