The action of 2:4-dinitrophenol on myosin and mitochondrial adenosine triphosphatase systems

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Abstract
In confirmation of Webster''s (1953) finding, 2:4-dinitrophenol is shown to stimulate the calcium-activated adenosine triphosphatase (ATPase) of myosin. The stimulation amounted to 100-150% under optimum conditions, and at 20 occurred when the ionic strength was varied over the range of approximately 0.06-0.46. When actin was present in a medium of low ionic strength, 2:4-dinitrophenol inhibited the calcium-activated ATPase of myosin. 2:4-dinitrophenol stimulated the calcium-activated ATPase of myofibrils at ionic strength of about 0.16 and higher. At 0[degree] the ionic strength had to be raised to about 0.4 and higher to obtain stimulation of the calcium-activated ATPase activity of L-myosin and myofibrils by 2:4-dinitrophenol. The pattern of Ca activation of the myofibrillar ATPase was similar at 0[degree] and 20[degree]. In contrast, whereas Mg strongly activated at 20[degree], at 0[degree] it produced little or no activation of rabbit-myofibrillar or rat-liver mitochondrial ATPases. Some effects of the action of 2:4-dinitrophenol on the rabbit-myofibrillar and the rat-liver mitochondrial ATPases are compared and discussed.