Free energy and enthalpy of ATP hydrolysis in the sarcoplasm

Abstract A rigorous calculation of the free energy available in vivo from ATP hydrolysis requires the following information which is not all available, namely: (i) intra­cellular pH, (ii) activities of all the species of reactants and products in sarcoplasm, (iii) thermodynamic data for all the reactions involved, including values for ionic strength and temperature dependence, and (iv) the extent of deviation from equilibrium conditions, i. e. during contraction. We shall discuss each of these factors in turn and state the assumptions made that allow the approximate calculation of the free energy made available by the following net reaction in the sarcoplasm: ATP +H2O → ADP + Pi + H+. (1) Although it can only be an approximation this calculation is useful since it will take into account recent thermodynamic measurements in vitro.