Thermochemistry of the Reaction {Phosphoenolpyruvate(aq) + D-Erythrose 4-Phosphate(aq) + H2O(1) = 2-Dehydro-3-Deoxy-D-Arabino-Heptonate 7-Phosphate(aq) + Phosphate(aq)}

Published: December 01, 2001

Author(s)

Yadu D. Tewari, N Kishore, R H. Bauerle, W R. LaCourse, Robert N. Goldberg

Abstract

Microcalorimetry and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of the biochemical reaction {phosphoenolpyruvate(aq) + D-erythrose 4-phosphate(aq) + H2O(l) = 2-dehydro-3-deoxy-D-arabino-heptonate 7-phosphate(aq) + phosphate(aq)}, the first step in the metabolic pathway leading to the biosynthesis of chorismate. DAHP synthase, the enzyme used to carry out this reaction, was prepared by using molecular biology techniques and then isolated in a highly purified form. The h.p.l.c. was used to establish that this reaction went to completion and that the apparent equilibrium constant K'(T = 298.15 K, pH {nearly equal to} 8.2) is > 1.4 103. The calorimetrically determined molar enthalpy for this biochemical reaction is δrHm(cal) = -(67.7 1.5) kJ mol-1 at T = 298.15 K, pH = 8.18, and ionic strength Im = 0.090 mol kg-1. Use of this result together with a chemical equilibrium model led to the standard molar enthalpy of reaction δrH o/m = -(70.0 3.0) kJ mol-1 at T = 298.15 K and Im = 0 for the chemical reference reaction {phosphoenolpyruvate3- (aq) + D-erythrose 4-phosphate2-(aq) + H2O(l) = 2-dehydro-3-deoxy-D-arabino-heptonate 7-phosphate 3-(aq) + HPO-(aq)}. Use of an estimated value of the standard molar entropy change δrSo/m for this reaction together with the measured value of δrHo/m yielded the standard molar Gibbs free energy change δrGo/m {nearly equal to} -39 kJ mol-1 and K {nearly equal to} 7 106 for the chemical reference reaction at T = 298.15 K and Im = 0. Some insight into the thermochemistry of this reaction has been obtained by assessing the contributions to δrHo/m that correspond to the loss of a phosphate from phosphoenolpyruvate and to the addition of a pyruvate group to D-erythrose 4-phosphate.
Citation: Journal of Chemical Thermodynamics
Volume: 33
Issue: 12
Pub Type: Journals

Keywords

2-dehydro-3-deoxy-D-arabino-heptonate 7-, apparent equilibrium constant, D-erythrose 4-phosphate, DAHP synthase, enthalpy, entropy, Gibbs free energy, phosphoenolpyruvate
Created December 01, 2001, Updated February 17, 2017