Open AccessThermodynamic analysis of the binding of glutathione to glutathione S ‐transferase over a range of temperatures
Author(s) -
OrtizSalmerón Emilia,
Yassin Zeyad,
ClementeJimenez M. Jose,
Las HerasVazquez F. Javier,
RodriguezVico Felipe,
Barón Carmen,
GarcíaFuentes Luis
Publication year - 2001
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2001.02349.x
Subject(s) - isothermal titration calorimetry , chemistry , enthalpy , glutathione , heat capacity , atmospheric temperature range , dimer , calorimetry , thermodynamics , biochemistry , enzyme , organic chemistry , physics
The binding properties of a glutathione S ‐transferase (EC 2.5.1.18) from Schistosoma japonicum to substrate glutathione (GSH) has been investigated by intrinsic fluorescence and isothermal titration calorimetry (ITC) at pH 6.5 over a temperature range of 15–30 °C. Calorimetric measurements in various buffer systems with different ionization heats suggest that protons are released during the binding of GSH at pH 6.5. We have also studied the effect of pH on the thermodynamics of GSH–GST interaction. The behaviour shown at different pHs indicates that at least three groups must participate in the exchange of protons. Fluorimetric and calorimetric measurements indicate that GSH binds to two sites in the dimer of 26‐kDa glutathione S ‐transferase from Schistosoma japonicum (SjGST). On the other hand, noncooperativity for substrate binding to SjGST was detected over a temperature range of 15–30 °C. Among thermodynamic parameters, whereas Δ G ° remains practically invariant as a function of temperature, Δ H and Δ S ° both decrease with an increase in temperature. While the binding is enthalpically favorable at all temperatures studied, at temperatures below 25 °C, Δ G ° is also favoured by entropic contributions. As the temperature increases, the entropic contributions progressively decrease, attaining a value of zero at 24.3 °C, and then becoming unfavorable. During this transition, the enthalpic contributions become progressively favorable, resulting in an enthalpy–entropy compensation. The temperature dependence of the enthalpy change yields the heat capacity change (Δ C p °) of −0.238 ± 0.04 kcal per K per mol of GSH bound.