Key Points
- To investigate the enthalpy changes associated with each intermediate step of ATP hydrolysis catalyzed by myosin subfragment-1.
- Microcalorimetry was used to measure heat production during ATP hydrolysis in 0.1 M KCl with 0.01 M MgCl2 and 0.02 M Tris/HCl (pH 7.8) at 23°C.
- Enthalpy values for ATP binding, cleavage, and product release were determined and compared with values in free solution.
- Binding of ATP to Subfragment 1 is exothermic (enthalpy change = -90 kJ/mol).
- Cleavage of ATP is endothermic (enthalpy change = +83 kJ/mol), contrary to the exothermic nature of free solution ATP hydrolysis.
- Pi release is strongly exothermic (enthalpy change = -88 kJ/mol), while dissociation of ADP is endothermic (enthalpy change = +72 kJ/mol).
Structured PICO
PPopulationMyosin subfragment-1 in 0.1 M KCl containing 0.01 M MgCl2 and 0.02 M Tris/HCl (pH 7.8) at 23°C
IInterventionATP hydrolysis catalyzed by myosin subfragment-1
CComparatorATP hydrolysis in free solution
OOutcomeEnthalpy changes (heat production) during intermediate steps of ATP hydrolysissurrogate
Large enthalpy changes accompany several intermediate steps of the myosin-catalyzed ATP hydrolysis cycle, reflecting its energy transduction role in muscle contraction.