Calculation of standard transformed Gibbs energies and standard transformed enthalpies of biochemical reactants.

The standard Gibbs energies of formation and standard enthalpies of formation of species involved in biochemical reactions are used to calculate standard transformed Gibbs energies of formation and standard transformed enthalpies of formation of 53 reactants (sums of species) at 298.15 K, pH 7, and ionic strengths of 0, 0.1, and 0. 25 M. The standard transformed Gibbs energies of formation are used to calculate apparent equilibrium constants K' for 22 biochemical reactions for which apparent equilibrium constants have been determined close to these conditions. This comparison is generally satisfactory given the differences in experimental conditions. The transformed formation properties for the 53 reactants make it possible to calculate transformed formation properties for other reactants involved in biochemical reactions with some of these reactants. This is illustrated by calculating standard transformed Gibbs energies of formation for 11 more reactants without information on the standard Gibbs energies of formation of the species. The list of 64 reactants for which standard transformed Gibbs energies of formation are presented can be considerably extended. The use of tables of standard transformed Gibbs energies of formation to store information on apparent equilibrium constants is more efficient than simply storing apparent equilibrium constants because a reactant can be looked up in a table and may be involved in hundreds of reactions. The effects of magnesium ions on several reactions involving ATP are calculated. The advantages of using enzyme-catalyzed reactions for determining thermodynamic properties of complicated molecules in aqueous solution are discussed. Copyright 1998 Academic Press.