THE INFLUENCE OF HYDROGEN ION CONCENTRATION ON THE MYOSIN-CATALYZED HYDROLYSIS OF ADENOSINE TRIPHOSPHATE

Abstract

The Michaelis constants for the system myosin–ATP have been measured at 5 °C and 15 °C from pH 7.0 to pH 10.5, in the presence of 0.4 M potassium chloride and 0.005 M calcium chloride. The experimental data point to the presence, in the active center, of two ionizable groups, with experimental acid pK of 7.35 and 8.6 respectively at 15 °C. The apparent heats of ionization of these groups are about 9 kcal/mole for the first one and close to zero for the second. These data are interpreted as indication of the presence in the active center of myosin of a histidyl and a sulphydryl residue. A mechanism is proposed for the hydrolysis of ATP in the presence of myosin.