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

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Abstract
The transient phase of ATP hydrolysis (early burst) was investigated for myosin [M], heavy meromyosin (HMM) and subfragment 1 (S-1) over a range of temperatures and pH. [Rabbit skeletal muscle was used.] The burst size at pH 8, 20.degree. C, was 0.8-0.85, based on steady-state and transient measurements. The equilibrium constant for the enzyme substrate to enzyme-product transition was 0.85 .+-. 0.05. Both myosin heads underwent the rapid hydrolysis step and there were no significant differences for S-1 vs. HMM or M. The transient data were fitted reasonably well by a single rate process, but available evidence was consistent with some heterogeneity and a range of rate constants differing by a factor of 2. At pH 6.9 and 3.degree. C, the burst size was 0.5 and the hydrolysis was slower than the configuration change measured by fluorescence. The results were consistent with the kinetic scheme .**GRAPHIC**. [where the asterisks refer to the degree of fluorescence enhancement]. The lower burst at low temperature and pH was partly explained by a reduction in the equilibrium constant, K3 and ATP was synthesized on the enzyme by a pH-temperature jump.