The effect of leiotonin fraction on stably phosphorylated smooth muscle myosin

This study was designed to determine the effect of leiotonin on the actin-activation once the myosin is stably phosphorylated. Gizzard myosin was stably phosphorylated by ATP-gamma-S using the gizzard light chain kinase. Addition of leiotonin preparation to phosphorylated myosin reconstituted with actin and tropomyosin did not alter the ATPase activity. Furthermore, leiotonin did not confer the calcium sensitivity of the ATPase activity. These experiments show that the actin-activated ATPase activity of stably phosphorylated gizzard myosin is not altered by leiotonin.