Thermodynamic calculations of biochemical reaction systems at specified pH, pMg, and change in binding of hydrogen and magnesium ions

Abstract

AbstractEach metabolite in biochemical reaction may be available as an equilibrated mixture of different charged ions, and it is termed as “metabolite species.” At equilibrium, each metabolite is represented as pseudoisomer group of metabolite species. At constant pH condition, the number of hydrogen and magnesium ions in a particular biochemical reactant is constant. The conventional thermodynamic property does not signify the biochemical systems precisely. Therefore, transformed thermodynamic Gibbs free energy change of reactions must be used for biochemical systems. Gibbs free energy of formation ( ) of pseudoisomers of different biochemical reactants in glycolysis is calculated based on pKa. Transformed Gibbs energy change of all biochemical reactions involved in glycolysis is calculated by incorporating pH, pMg, ionic strength, and change in binding of H+ and Mg2+ ions. The transformed Gibbs free energy change of all biochemical reactions in glycolysis (ΔrG′0) is calculated and compared with standard Gibbs free energy change of reaction (ΔrG0). The results indicated that there is difference in values of (ΔrG′0) and (ΔrG0). Hence, it is shown that the thermodynamic property G is not sufficient to provide a criterion for the spontaneity of biochemical reaction. At equilibrium, G′ must be minimized rather than G at constant pH and pMg.