Equilibrium measurements at several temperatures between 293 K and 308 K have been performed on the tannase catalyzed reaction: 3,4,5-trihydroxybenzoic acid propyl ester(sln) + H2O(sln) = 3,4,5-trihydroxybenzoic acid(sln) + propan-1-ol(sln), where sln = aqueous phosphate buffer, aqueous acetate buffer, and toluene. The change in binding of the hydrogen ion DrN(H + ) for this biochemical reaction in aqueous solution was calculated both from an equilibrium model for the biochemical reaction and from the dependence of the apparent equilibrium constant on pH. Calorimetric measurements were also performed for this biochemical reaction in aqueous phosphate and 2-(N-morpholino)ethanesulfonic acid (MES) buffers. Standard transformed thermodynamic quantities for the overall biochemical reaction as well as standard thermodynamic quantities for chemical reference reactions that involve specific chemical species have been calculated from the experimental results. It was found that the equilibrium yield of 3,4,5-trihydroxybenzoic acid propyl ester is significantly enhanced by carrying out the reaction in toluene rather than in the aqueous buffered solutions. The standard molar enthalpy change DrH°m for the dissociation reaction MES 2 (aq) = MES -(aq) + H + (aq) has been measured calorimetrically and is -(15.020.1)kJ•mol -1 at the temperature T = 298.15 K and ionic strength I = 0.