Thermodynamics of Reactions Catalyzed by Branched-Chain-Amino-Acid Transaminase
Yadu D. Tewari, Robert N. Goldberg, J D. Rozzell
Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for reactions catalyzed by branched-chain-amino-acid transaminase. The following biochemical reactions have been studied at the temperature 298.15 K and in the pH range (7.15 to 7.24): L-valine(aq) + 2-oxoglutarate(aq) = 2-oxoisovalerate(aq) + L-glutamate(aq); L-leucine(aq) + 2-oxoglutarate(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,δrHo/m entropy, δrSo/m and Gibbs free energy δrGo/m changes for reference reactions involving specific species. Apparent equilibrium constants and standard transformed Gibbs energy changes for these reactions under physiological conditions have also been calculated. The use of these results for optimization of product yields of the branched-chain amino acids is discussed.