An investigation of the equilibrium of the reaction {L-aspartate(aq) plus 2-oxoglutarate(aq) = oxaloacetate(aq) plus L-glutamate(aq)}

Apparent equilibrium constants have been measured for the following biochem ical reaction: L-aspartate(aq) + 2-oxoglutarate(aq) = oxaloacetate(aq) + L-glutamate (aq). This reaction, catalysed by aspartate transaminase, alas studied over the r anges 283.15 less than or equal to T/K less than or equal to 303.15, 6.94 l ess than or equal to pH less than or equal to 7.13, and 0.163 less than or equal to I-m/(mol.kg(-1)) less than or equal to 0.167, where T is temperatu re and I-m is ionic strength. The instability of the oxaloacetate in soluti on required the use of an experimental procedure that was brief. Thus, the procedure used was to measure the change in the chromatographic response De lta R of the oxaloacetate chromatographic peak that accompanied the reactio n. Values of Delta R were measured for several solutions under near equilib rium conditions. The chromatographic response Delta R is expected to be zer o for a solution that is at equilibrium with regard to the above reaction a nd prior to the addition of the enzyme. The results were used to calculate the standard molar Gibbs energy change Delta(r)G(m)degrees = (4.82 + 0.21) kJ.mol(-1), the equilibrium constant K = (0.143 +/- 0.012), the standard mo lar enthalpy change Delta(r)H(m)degrees = (1.9 +/- 2.9) kJ.mol(-1), and the standard molar entropy change Delta(r)S(m)degrees = -(10 +/- 10) J.K-1.mol (-1) for the following chemical reference reaction at T = 298.15 K and I-m = 0: L-aspartate(-) (aq) + 2-oxoglutarate(2-) (aq) = oxaloacetate(2-) (aq) + L-g lutamate(-) (aq). Under near physiological conditions (T = 311.15 K, pH = 7.0, I-m = 0.25 mol .kg(-1)) the apparent equilibrium constant K' for the overall biochemical r eaction is calculated to have the value 0.147; the standard transformed Gib bs energy change Delta(r)G(m)'degrees = 4.96 kJ.mol(-1) under these conditi ons. (C) 1998 Academic Press.