Early phosphate burst of heart myosins- Phylogenic variations

The phosphate burst of cardiac myosins from different animal species was studied by a rapid quench-flow technique. The rate constant of the phosphate burst varied from one species to another. Moreover it was lower for cardiac myosins than for skeletal myosin. The phosphate burst rate correlated with the ATPase in the steady state and with the muscle-shortening speed. By contrast, the amplitude of the phosphate burst did not vary significantly. Its value was 0.8--0.9 per myosin site for each of the myosins studied. Deviations from this stoichiometry were related to the mode of preparation of the myosin and to denaturation by a high pH.