Key result
The enthalpy of binding of myosin-S1 to F-actin was +22 to +27 kJ/mol at 12°C and +26 kJ/mol at 0°C, while HMM binding to actin at 12°C was +26 kJ/mol of myosin head.
The study provides thermodynamic parameters (enthalpy and entropy) for the binding of rabbit skeletal myosin subfragment 1 and heavy meromyosin to F-actin.
Provides thermodynamic parameters for actomyosin binding; leaves open relevance to human cardiac myosin function.
The heat of binding of rabbit skeletal myosin subfragment 1 (myosin-S1) and heavy meromyosin (HMM) to F-actin has been measured by batch calorimetry. Proton release measurements in unbuffered solutions indicate that less than 0.1 mol of protons is absorbed or released per mol of myosin head bound to actin. Hence, the measured heats are approximately equal to the enthalpy of myosin-S1 and HMM binding to actin. The enthalpy of binding of myosin-S1 to actin was +22 +/- 3 and +27 +/- 5 kJ/mol of myosin-S1 in two series of experiments at 12 degrees C and +26 +/- 5 kJ/mol of myosin-S1 at 0 degrees C, indicating that delta Cp for this reaction in the range of 0-12 degrees C is small (-80 J/mol/K). The enthalpy of binding of HMM to actin at 12 degrees C was found to be +26 +/- 1 kJ/mol of myosin head. The enthalpies determined here and the equilibrium constants obtained from the literature for measurements at 20 degrees C under identical solvent conditions were used to estimate the entropy of the association of myosin S1 and HMM with F-actin: +235 J/mol/K for myosin-S1 and +190 J/mol of myosin head/K for HMM. Thermodynamic parameters of the interaction of myosin-S1 with actin and ADP or AMP-PNP can be evaluated using the enthalpy of association of myosin-S1 with actin determined here, together with literature values for the equilibrium constants and enthalpies of binding of these nucleotides to myosin-S1. The calculated enthalpies of binding of ADP or AMP-PNP to actomyosin-S1 are small and negative.
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Smith et al. (1984) studied this question. Myosin-S1 and HMM binding to F-actin was evaluated on Enthalpy of binding. The enthalpy of binding of myosin-S1 to F-actin was +22 to +27 kJ/mol at 12°C and +26 kJ/mol at 0°C, while HMM binding to actin at 12°C was +26 kJ/mol of myosin head.
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