Microcalorimetry and high-performance liquid chromatography (HPLC) have been used to conduct a thermodynamic investigation of the reaction: {methyl ferulate(aq) + H2O(1) = methanol(aq) + ferulic acid(aq)}, as catalyzed by feruloyl esterase. Values of the apparent equilibrium constant K' = (29.6 +/- 0.7) (T = 298.15 K, citrate buffer at pH 4.98, ionic strength I = 0.39 mol . kg(-1)) and of the calorimetrically determined enthalpy of reaction Delta H-r(cal) = (4.0 +/- 0.9) kJ . mol(-1) (T = 298.15 K and citrate buffer at pH 4.81, I = 0.36 mol . kg-1) were measured. A chemical equilibrium model, together with pKs and standard enthalpies of reaction Delta H-r degrees for the H+(aq) binding reactions of the reactants and products, was then used to calculate the values K = (1.89 +/- 0.06) . 10(-4), Delta H-r degrees = (7.3 +/- 1.7) kJ . mol(-1), Delta(r)G degrees =(21.25 +/- 0.07) kJ . mol(-1), and Delta S-r degrees = -(46.8 +/- 5.7) J . K-1 . mol(-1) for the chemical reference reaction {methyl ferulate(aq) + H2O(1) = methanol(aq) + ferulic acid(-)(aq) + H+(aq)}. These values of K and Delta H-r degrees are similar in magnitude to the corresponding values reported for the reaction {propyl gallate(aq) + H2O(1) = 3,4,5-trihydroxybenzoic acid(-)(aq) + 1-propanol(aq) + H+(aq)}. The results obtained in this study can be used in a chemical equilibrium model to calculate how K' and other standard transformed properties such as the standard transformed enthalpy Delta H-r'degrees, standard transformed Gibbs free energy Delta(r)G'degrees, and the change in binding of H+(aq), Delta N-r(H+), vary with the independent variables T, pH, and I. (C) 2010 Elsevier Ltd. All rights reserved.