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Thermodynamics of the oxidation-reduction reaction {2 glutathione(red)(aq)+NADP (ox)(aq)=glutathione(ox)(aq) + NADP(red)(aq)}

Published

Author(s)

Yadu D. Tewari, Robert N. Goldberg

Abstract

Microcalorimetry, spectrophotometry, and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of the glutathione reductase catalyzed reaction {2 glutathionered(aq) + NADPox(aq) = glutathioneox(aq) + NADPred(aq)}. The reaction involves the breaking of a disulfide bond and is of particular importance because of the role glutathionered plays in the repair of enzymes. Values of the apparent equilibrium constant K' were measured over a range of temperature (288.15 K to 303.15 K), pH (6.58 to 8.68), and ionic strength Im (0.091 mol kg-1 to 0.90 mol kg-1). The results of the equilibrium and calorimetric measurements were analyzed in terms of a chemical equilibrium model that accounts for the multiplicity of ionic states of the reactants and products. These calculations led to values of thermodynamic quantities at T = 298.15 K and Im = 0 for a chemical reference reaction that involves specific ionic forms. Thus, for the reaction {2 glutathioner-ed(aq) + NADPox3-(aq) = glutathioneox2-(aq) + NADPre4-d(aq) + H+(aq)}, the equilibrium constant K = (6.6 4.4) 10-11, the standard molar enthalpy of reaction DrH m = (6.9 3.0) kJ mol-1, the standard molar Gibbs free energy change DrG m = (58.1 1.7) kJ mol-1, and the standard molar entropy change DrS m = -(172 12) J K-1 mol-1. Under approximately physiological conditions (T = 311.15 K, pH = 7.0, and Im = 0.25 mol kg-1) the apparent equilibrium constant K' 0.013. The results of the several studies of this reaction from the literature have also been examined and analyzed using the chemical equilibrium model. It was found that much of the literature is in agreement with the results of this study. Use of our results together with a value from the literature for the standard electromotive force E for the NADP redox reaction leads to E = +0.166 V (T = 298.15 K and I = 0) for the glutathione redox reaction {glutathioneox2-(aq) + 2 H+(aq) + 2 e- = 2 glutathioner-ed(aq)}. The thermodynamic results obtained in this study also permit the calculation of the standard apparent electromotive force E' for the biochemical redox reaction {glutathioneox(aq) + 2 e- = 2 glutathionered(aq)}over a wide range of temperature, pH, and ionic strength. At T = 298.15 K, I = 0.25 mol kg-1, and pH = 7.0, the calculated value of E' is -0.265 V.
Citation
Journal of Chemical Thermodynamics
Volume
35
Issue
8

Keywords

apparent equilibrium constant, chemical thermodynamics, enthalpy, entropy, Gibbs free energy, glutathione reductase, NADP, Β-nicotinamide adenine dinucleotide

Citation

Tewari, Y. and Goldberg, R. (2003), Thermodynamics of the oxidation-reduction reaction {2 glutathione(red)(aq)+NADP (ox)(aq)=glutathione(ox)(aq) + NADP(red)(aq)}, Journal of Chemical Thermodynamics (Accessed July 13, 2024)

Issues

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Created August 1, 2003, Updated February 17, 2017