Adenosine Triphosphate-dependent Reaction of 1-Fluoro-2,4-dinitrobenzene with Various Myosins

The activating effect of free ATP and the inhibitory effect of MgATP2- on the incorporation of 1-fluoro-2,4-dinitrobenzene into myosin were compared in skeletal and cardiac muscle of the rabbit, skeletal and smooth muscle of the chicken, and skeletal muscle of the cat and sloth. In all cases, the myosin with low ATPase activity (from rabbit cardiac, chicken smooth, and sloth skeletal muscle) showed less change in the ATP-mediated dinitrophenylation than the myosin with high ATPase activity (from rabbit, chicken, and cat skeletal muscle). Furthermore, no inhibitory effect of MgATP2- on the dinitrophenylation of chicken gizzard myosin was observed. These differences were found over a wide concentration range of free ATP, MgATP2-, ATP derivatives, and nucleoside triphosphates. It was concluded that the ATP-induced conformational change varies from one myosin to another. The relationship between ATP-induced changes in the dinitrophenylation of rabbit skeletal myosin and ATPase activity of this myosin was studied. The activating effect of free ATP on the incorporation of 1-fluoro-2,4-dinitrobenzene into myosin was less affected by various treatments than the ATPase activities of myosin. The inhibitory effect of MgATP2- on the dinitrophenylation of myosin was related to the inhibition of the actin- and Mg2+-activated ATPase activity of myosin produced by different agents and modification with iodoacetate. However, the MgATP2--regulated dinitrophenylation of myosin was more readily abolished by iodoacetamide or trinitrobenzenesulfonate than the actinand Mg2+-activated ATPase activity of myosin. These results indicate that the ATP-induced changes in the dinitrophenylation of myosin do not occur at the ATPase site. The incorporation of 1-fluoro-2,4-dinitrobenzene into several ATP-utilizing enzymes other than myosin was not increased by free ATP or decreased by MgATP2-.