A thermodynamic study of the conversion of chorismate to isochorismate

Microcalorimetry and high performance liquid chromatography were used to co nduct a thermodynamic investigation of the biochemical reaction chorismate( aq) = isochorismate(aq). This reaction occurs at the branch point of the ch orismate metabolic pathway that leads to the synthesis of enterobactin. Iso chorismate synthase, the enzyme that catalyzes this reaction, was prepared for this study by using molecular biology techniques. The equilibrium and c alorimetric measurements were performed at T = 298.15 K and at the respecti ve pHs 7.34 and 6.93. For the chemical reference reaction chorismate(2-)(aq ) = isochorismate(2-)(aq), the equilibrium constant K = (0.84 +/- 0.04) and the standard molar enthalpy of reaction Delta(r)H(m)(O) = -(0.81 +/- 0.27) kJ . mol(-1) at T = 298.15 K and ionic strength I-m = 0. Under approximate ly physiological conditions, die apparent equilibrium constant K' = 0.83 an d the standard transformed gibbs energy change Delta(r)G'(O)(m) = 0.48 kJ . mol(-1) for the overall biochemical reaction. (C) 2000 Academic Press.