Transient phase of adenosine triphosphate hydrolysis by myosin, heavy meromyosin, and subfragment 1

The transient phase of adenosine triphosphate (ATP) hydrolysis (early burst) was investigated for myosin, heavy meromyosin (HMM), and subfragment 1 (S-1) over a range of temperatures and pH's. The burst size at pH 8,20 degrees C, is 0.8-0.85, based on steady-state and transient measurements. The equilibrium constant for the enzyme-substrate to enzyme-product transition is 0.85 +/- 0.05. It is concluded that both myosin heads undergo the rapid hydrolysis step and that there are no significant differences for S-1 vs. HMM or myosin. The transient data are fitted reasonably well by a single rate process, but available evidence is consistent with some heterogeneity and a range of rate constants differing by a factor of two. At pH 6.9 and 3 degrees C, the burst size is 0.5 and the hydrolysis is slower than the configuration change measured by fluorescence. The results are consistent with the kinetic scheme (see article). The lower burst at low temperature and pH can be partly explained by a reduction in the equilibrium constant, K3, and ATP can be synthesized on the enzyme by a pH-temperature jump.