Effect of dinitrophenol on the interaction between myosin and nucleotides.

Webster (1) first noticed that 2,4-dinitrophenol increased the ATPase” activity of myosin. Attention was focused on this observation by the work of Greville and Needham (2) and Chappell and Perry (3), who showed that under certain conditions DNP accelerated the ATPase activity of myosin A, myosin B, and myofibrils, whereas the ITPase activity was inhibited. They noted the similarity between their results and the known effects of DNP on mitochondrial ATPase activity (4, 5). Upon examination of these findings, it occurred to us that with the aid of a kinetic scheme already used to interpret certain enzymic and light-scattering studies on myosin (6), one could explain in a qualitative fashion some of the observed effects of DNP on ATPase and ITPase activity. If these ideas were relevant, then it was also of interest to examine the effects of DNP on some other nucleotides, and to attempt to correlate the enzymic data with concomitant contmctile data. Such studies might shed more light not only on the nature of the enzymic site and its mode of interaction with the substrate molecule, but also might be of value in elucidating the nature of the mechanochemical coupling.