The study directly observed the endothermic on-enzyme ATP-cleavage step of myosin subfragment 1 and demonstrated proton involvement in all four principal steps of the ATPase reaction.
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No immediate implications for cardiac myosin therapies; leaves open the in vivo significance of proton-linked ATPase steps.
The enthalpy changes during individual reaction steps of the myosin subfragment 1 ATPase were studied with the use of a new stopped-flow calorimeter [Howarth, Millar & Gutfreund (1987) Biochem. J. 248, 677-682]. 2. At 5 degrees C and pH 7.0, the endothermic on-enzyme ATP-cleavage step was observed directly (delta H = +64 kJ.mol-1). 3. ADP binding is accompanied by a biphasic enthalpy change. 4. The release and uptake of protons was investigated by the use of two buffers with widely different heats of ionization. 5. Protons are involved in all four principal steps of the myosin subfragment 1 ATPase.
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Millar et al. (1987) studied this question.
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