The mechanism of the skeletal muscle myosin ATPase. III. Relationship of the H+ release and the protein absorbance change induced by ATP to the initial Pi burst.

Several phenomena are associated with the binding of ATP to myosin: 1) a fluorescence enhancement, 2) a release of H+, and 3) a protein absorbance change. In the accompanying paper (Chock, S. P., Chock, P. B., and Eisenberg, E. (1979) J. Biol. Chem. 254, 3236-3243), it was demonstrated that the fluorescence enhancement is mainly caused by the hydrolysis of ATP in the initial Pi burst rather than by the conformational change induced by the irreversible binding of ATP. In the present study, the cause of the H+ release and the protein absorbance change were investigated. The results show that like the rate of the fluorescence enhancement the rates of the H+ release and the protein absorbance change level off at high ATP concentration at a much lower rate than the rate of irreversible ATP binding. Furthermore, under all conditions tested, the rates of the H+ release and the protein absorbance change are equal to the rate of the initial Pi burst. Therefore, like the fluorescence enhancement, most of the H+ release and the protein absorbance change are associated with the initial Pi burst rather than the binding of ATP.