2627-73-8Relevant articles and documents
A thermodynamic study of the reactions: {2-dehydro-3-deoxy-D-arabino-heptanoate 7-phosphate(aq) = 3-dehydroquinate(aq) + phosphate(aq)} and {3-dehydroquinate(aq) = 3-dehydroshikimate(aq) + H2O(l)}
Tewari, Yadu B.,Goldberg, Robert N.,Hawkins, Alastair R.,Lamb, Heather K.
, p. 1671 - 1691 (2007/10/03)
Microcalorimetry and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of reactions catalyzed by 3-dehydroquinate synthase and by 3-dehydroquinate dehydratase. These are the second and third reactions in the metabolic pathway leading to the formation of chorismate. The two reactions are: {DAHP(aq) = 3-dehydroquinate(aq) + phosphate(aq)} and {3-dehydroquinate(aq) = 3-dehydroshikimate(aq) + H2O(l)}. The h.p.l.c. measurements showed that the first reaction proceeded to completion and that the value of the apparent equilibrium constant for the second reaction was K′ = (4.6 ± 1.5) (Hepes buffer, temperature T = 298.15 K, pH = 7.50, and ionic strength Im = 0.065 mol·kg-1). Calorimetric measurements led to a molar enthalpy of reaction ΔrHm (cal) = -(50.9 ± 1.1) kJ·mol-1 (Hepes buffer, T = 298.15 K, pH = 7.46, Im = 0.070 mol·kg-1) for the first reaction and to ΔrHm (cal) = (2.3 ± 2.3) kJ·mol-1 (Hepes buffer, T = 298.15 K, pH = 7.42, Im = 0.069 mol·kg-1) for the second reaction. These results were analyzed in terms of a chemical equilibrium model that accounts for the multiplicity of ionic states of the reactants and products. These calculations gave thermodynamic quantities at T = 298.15 K and Im = 0 for chemical reference reactions involving specific ionic forms. For the reaction DAHP3-(aq) = 3-dehydroquinate-(aq) + HPO42-(aq), the standard molar enthalpy of reaction ΔrHmo = -(51.1 ± 4.5) kJ·mol-1. For the reaction 3-de-hydroquinate(aq) = (3-dehydroshikimate(aq) + H2O(l), the equilibrium constant K = (4.6 ± 1.5) and ΔrHmo = (2.3 ± 2.3) kJ·mol-1. A Benson type approach was used to estimate the standard molar entropy change ΔrSmo for the first reference reaction and led to the value K ≈ 2·1014 for this reaction. Values of the apparent equilibrium constants and the standard transformed Gibbs free energy changes ΔrGmo under approximately physiological conditions are given for the biochemical reactions.