Thermochemistry of the Biochemical Reaction: {pyrophosphate(aq) + H2O(l) = 2 phosphate(aq)}

Published

June 1, 2002

Author(s)

Robert N. Goldberg, Yadu D. Tewari

Abstract

Calorimetric enthalpies of reaction have been measured for the overall biochemical reaction {pyrophosphate(aq) + H₂O(l) = phosphate(aq)}. The reaction was catalyzed by alkaline phosphatase and to simplify the thermochemistry, was carried out in the absence of Mg²⁺(aq). Measurements were performed with phosphate buffer (pH = 7.19 and pH = 7.94), PIPES buffer (pH = 7.13), and HEPES buffer (pH = 7.86). The results of these measurements were analyzed by using an equilibrium model. These calculations lead to the standard molar enthalpy change {Δ}_rH^°_m = -(17.3 0.6) kJ mol^-1 (temperature T = 298.15 K and ionic strength I = 0) for the reference reaction {HP₂O^3-₇ (aq) + H₂O(l) = 2 HPO^2-₄(aq) + H⁺(aq)}. Values of the apparent equilibrium constant K' for the overall biochemical reaction from the literature were also analyzed by using the equilibrium model in order to obtain what is believed to be a reliable value for the equilibrium constant K = 4.7 10^-4 for the reference reaction. The values of K and {Δ}_rH^°_m for the reference reaction have been used together with values from the CODATA Tables to calculate standard molar formation properties for the pyrophosphate species.

Citation

Journal of Chemical Thermodynamics

Volume

34

Issue

6

Pub Type

Journals

Keywords

alkaline phosphatase, calorimetry, enthalpy, entropy, Gibbs free energy, phosphate

Citation

Goldberg, R. and Tewari, Y. (2002), Thermochemistry of the Biochemical Reaction: {pyrophosphate(aq) + H₂O(l) = 2 phosphate(aq)}, Journal of Chemical Thermodynamics (Accessed May 2, 2025)