Thermodynamics of the maleate and citraconate hydration reactions catalysed by malease from Pseudomonas pseudoalcaligenes

Malease from Pseudomonas pseudoalcaligenes catalyses the hydration of both maleate and citraconate to D‐malate and D‐citramalate, respectively. The K app for these hydration reactions were 2050 and 104, respectively, under standard biochemical conditions (25°C, pH 7.0, I = 0.1). The influence of the pH (6.0–8.5) on K app was determined. The Gibbs‐free‐energy changes under standard biochemical conditions for the hydration of the dianionic acids were calculated to be –19.28 kJ · mol −1 and –11.65 kJ · mol −1 , respectively. From the obtained data together with data from the literature, the Gibbs free energy of formation of maleate 2− and citraconate 2− were calculated to be ‐588.91 kJ · mol −1 and –600.56 kJ · mol −1 , respectively. The influence of the temperature (10–40°C) on K app was determined for both hydration reactions. The enthalpy change (Δ H° ′) and entropy change (Δ S°′ ) under standard biochemical conditions for the maleate 2− (Δ H°′ =−18.07 kJ · mol −1 , Δ S °′= 2.94 J · mol −1 · K −1 ) and citraconate 2− (Δ H° ′=−22.55 kJ · mol −1 , Δ S° ′=−35.92 kJ · mol −1 · K −1 ) hydration reactions were calculated. The reaction rate of malease from Ps. pseudoalcaligenes was studied for both hydration reactions as a function of temperature. From these studies, the Gibbs free energies of activation for the maleate and citraconate hydration reactions catalysed by malease from Ps. pseudoalcaligenes were calculated to be 62.21 kJ · mol −1 and 63.43 kJ · mol −1 , respectively.