Increase in the actin-activated Mg2+-ATPase activity of smooth muscle myosin by increasing myosin concentration.
The actin-activated Mg2+-ATPase activity of smooth muscle myosin was measured in 85 mM KCl, 6 mM MgCl2 in the absence of tropomyosin. The activity was dependent on myosin concentration. Vmax increased as myosin concentration was increased, while the Ka (the apparent dissociation constant for actin) remained the same. The extent of filament formation was also correlated with myosin concentration and most of the myosin monomers existed in 10S conformation. These results suggest that myosin concentration influences the actin-activated Mg2+-ATPase activity by changing the 10S-6S-filaments equilibrium.
Higashihara
M
M
Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106.
Ikebe
M
M
D000199:Actins / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D004789:Enzyme Activation; D005895:Gizzard, Avian / Q000201:enzymology; D007700:Kinetics; D009130:Muscle, Smooth / Q000201:enzymology; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits; D014422:Turkeys
D000199:Actins; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins