Kinetics and Substrate Binding of Myosin Adenosine Triphosphatase

Abstract The rate of hydrolysis of adenosine triphosphate and the binding of inorganic pyrophosphate to myosin vary inversely with increasing concentration of free Mg++, in the presence of a magnesium ethylenediaminetetraacetate buffer system; half-maximum binding of pyrophosphate and 50% inhibition of adenosine triphosphatase activity occur at a free Mg++ concentration about 10-7 m at 3°. The binding of pyrophosphate to myosin is reduced if Ca++ replaces Mg++ in the medium; it is also reduced by lowering the pH or raising the temperature. Actin is a competitive inhibitor of pyrophosphate binding to myosin. The actin-myosin interaction requires firmly bound Mg++. 2,4-Dinitrophenol has no effect on pyrophosphate binding to myosin. A hypothesis is presented, on the basis of the above data, which gives a simple explanation of the effects of Mg++, Ca++, ethylenediaminetetraacetate, and actin on the adenosine triphosphatase activity of myosin.