THERMODYNAMICS OF THE MALEATE AND CITRACONATE HYDRATION REACTIONS CATALYZED BY MALEASE FROM PSEUDOMONAS-PSEUDOALCALIGENES

Malease from Pseudomonas pseudoalcaligenes catalyses the hydration of both maleate and citraconate to D-malate and D-citramalate, respective ly. The K(app) for these hydration reactions were 2050 and 104, respec tively, under standard biochemical conditions (25-degrees-C, pH 7.0, I = 0.1). The influence of the pH (6.0-8.5) on K(app) was determined. T he 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 to gether with data from the literature, the Gibbs free energy of formati on of maleate2- and citraconate2 were calculated to be -588.91 kJ . mo l-1 and -600.56 kJ . mol-1, respectively. The influence of the tempera ture (10-40-degrees-C) on K(app) was determined for both hydration rea ctions. The enthalpy change (DELTAH-degrees') and entropy change (DELT AS-degrees') under standard biochemical conditions for the maleate2- ( DELTAH-degrees' = -18.07 kJ . mol-1, DELTAS-degrees' = 2.94 J . mol-1 . K-1) and citraconate2- (DELTAH-degrees' = -22.55 kJ . mol-1, DELTAS- degrees' = -35.92 kJ . mol-1 . K-1) hydration reactions were calculate d. 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 ci traconate hydration reactions catalysed by malease from Ps. pseudoalca ligenes were calculated to be 62.21 kJ . mol-1 and 63.43 kJ . mol-1, r espectively.