(adenosine triphosphate/equilibrium constants/Gibbs energy of formation/enthalpy of formation/heat of reaction)

Equilibrium compositions of solutions of bio- chemical species can be calculated by use of general equilibrium computer programs that minimize the Gibbs energy. The standard Gibbs energies of formation and standard enthalpies of formation of the species in a biochemical system can be calculated by Gaussian reduction of the augmented transpose of the stoichiometric number matrix for the system. The conservation matrix, which is also needed for the calculation of the equilibrium composition, can be obtained in two ways. The hydrolysis of adenosine 5'-triphosphate in solutions containing magnesium ions can be treated by considering 17 species. The equilibrium composition and enthalpy are calculated before and after adding ATPase. This makes it possible to calculate ApH, ApMg, and the heat of reaction when ATPase is added. In making equilibrium calculations on biochemical reactions, the pH and concentrations of free metal ions that complex with the reactants are usually chosen as independent varia- bles, and an apparent equilibrium constant K' is defined in terms of total concentrations of the reactants (1). For exam- ple, for the hydrolysis of adenosine triphosphate to adenosine diphosphate and inorganic phosphate,