Effect of Temperature on the Standard Transformed Thermodynamic Properties of Biochemical Reactions with Emphasis on the Maxwell Equations

Abstract

When the standard transformed Gibbs energy (ΔfG‘°) of formation of a reactant (sum of species) in an enzyme-catalyzed reaction can be expressed as a function of temperature, pH, and ionic strength, all the other standard transformed properties of the reactant (ΔfS‘°, ΔfH‘°, , and N̄H) can be calculated as functions of temperature, pH, and ionic strength by taking partial derivatives. Since there is very little data on heat capacities of species in biochemical reactions, the calculations presented here are based on the assumption that the heat capacities of species are equal to zero at zero ionic strength. The most basic data on a biochemical reactant consists of ΔfG°, ΔfH°, charge number, and number of hydrogen ions for the species involved. These data can be used to derive functions of temperature, pH, and ionic strength that give the standard transformed thermodynamic properties of reactants, such as ATP, ADP, H2O, and inorganic phosphate. This makes it possible to obtain the functions that represent ΔrG‘°, ΔrS‘°, ΔrH‘°, ΔrCP‘°, and ΔrNH for enzyme-catalyzed reactions, such as ATP + H2O = ADP + Pi. The calculations can be checked by testing that ΔrG‘° = ΔrH‘° − TΔrS‘° and the Maxwell equation connecting ΔrS‘° with ΔrNH is obeyed.