Thermodynamics of reactions catalysed by branched-chain-amino-acid transaminase

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for reaction a catalysed by branched-chain-amino-acid transa minase. The following biochemical reactions have been studied at the temper ature 298.15 K and in the pH range (7.15 to 7.24): L-valine(aq) + 2-oxoglut arate(aq) = 2-oxoisovalerate(aq) + L-glutamate(aq); L-leucine(aq) + 2-oxogl utarate(aq) = 2-oxoisocaproate(aq) + L-glutamate(aq); and L-tert-leucine(aq ) + 2-oxoglutarate(aq) = 3,3-dimethyl-2-oxobutanoate(aq) + L-glutamate(aq). The results have been used to calculate equilibrium constants and standard molar enthalpy Delta H-r(m)o, entropy Delta S-r(m)o, and Gibbs free energy Delta (r)G(m)(o) changes for reference reactions involving specific specie s. Apparent equilibrium constants and standard transformed Gibbs free energ y changes for these reactions under physiological conditions have also been calculated. The use of these results fur optimization of product yields of the branched-chain amino acids is discussed. (C) 2000 Academic Press.