Use of standard Gibbs free energies and standard enthalpies of adenosine(aq) and adenine(aq) in the thermodynamics of enzyme-catalyzed reactions

Abstract

The recent determination [J. Chem. Thermodyn. 33 (2003) 1917] of third law entropies and other calorimetric properties of adenine has provided new values for Δ f G m ∘(adenine, aq) and Δ f H m ∘(adenine, aq). This makes it possible to calculate new values of Δ f G m ∘ and Δ f H m ∘ for the species adenine 0 and Hadenine +. New values have also been calculated for d-ribose(aq) and the species of d-ribose 1-phosphate(aq) and d-ribose 5-phosphate(aq). To make calculations on reactants (sum of species) at specified pH, it is necessary to calculate standard transformed Gibbs free energies of formation Δ f G ′∘ m and standard transformed enthalpies of formation Δ f H ′∘ m of the pseudoisomer groups adenine, d-ribose, d-ribose 1-phosphate, and d-ribose 5-phosphate at specified temperatures, pHs, and ionic strengths. These transformed thermodynamic properties are used to calculate apparent equilibrium constants K ′, Δ r G ′∘ m, Δ r H ′∘ m, Δ r S ′∘ m, and changes in the binding of hydrogen ions Δ r N H in two enzyme-catalyzed reactions involving adenosine and adenine. The apparent equilibrium constants calculated using calorimetric data are in agreement with experimental values determined in 1980. The calculation of transformed thermodynamic properties at various temperatures, pHs, and ionic strengths is quite complicated, so the symbolic facilities of Mathematica R are used to derive functions, calculate partial derivatives, make tables, and calculate plots.