M José Clemente-Jiménez

Universidad de Almería, Almería, Andalusia, Spain

Are you M José Clemente-Jiménez?

Claim your profile

Publications (5)13.43 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The role of the hydroxyl group of tyrosine 6 in the binding of Schistosoma japonicum glutathione S-transferase has been investigated by isothermal titration calorimetry (ITC). A site-specific replacement of this residue with phenylalanine produces the Y6F mutant, which shows negative cooperativity for the binding of reduced glutathione (GSH). Calorimetric measurements indicated that the binding of GSH to Y6F dimer is enthalpically driven over the temperature range investigated. A concomitant net uptake of protons upon binding of GSH to Y6F mutant was detected carrying out calorimetric experiments in various buffer systems with different heats of ionization. The entropy change is favorable at temperatures below 26 degrees C for the first site, being entropically favorable at all temperatures studied for the second site. The enthalpy change of binding is strongly temperature-dependent, arising from a large negative DeltaC(o) (p1)=-3.45+/-0.62kJK(-1)mol(-1) for the first site, whereas a small DeltaC(o) (p2)=-0.33+/-0.05kJK(-1)mol(-1) for the second site was obtained. This large heat capacity change is indicative of conformational changes during the binding of substrate.
    International Journal of Biological Macromolecules 10/2003; 32(3-5):67-75. · 2.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: There has been some speculation about the salt independence of Schistosoma japonicum glutathione S-transferase (Sj26GST, EC. 2.5.1.18), but this aspect has not been carefully studied before. To establish the basis for a further development of this dependence, we have performed a methodical study of the influence of some important ions and their concentration on the binding properties of glutathione to Sj26GST by means of isothermal calorimetry and fluorescence quenching. Salts like NaCl, Na(2)SO(4) and MgSO(4) do not change practically the affinity of the protein for its substrate, whilst MgCl(2) has the effect of decreasing the affinity as its concentration rises. However, the enthalpy change is not affected by all the salts studied, and so, the entropy change is the causal factor in dropping the affinity. We also looked at the conformational stability of the protein under different conditions to check the structural changes they provide, and found that the unfolding parameters are practically not affected by the salt concentration. We discuss the results in terms of the chaotropic nature of the ions implied.
    International Journal of Biological Macromolecules 02/2003; 31(4-5):155-62. · 2.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 degrees 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 degrees C. Among thermodynamic parameters, whereas DeltaG degrees remains practically invariant as a function of temperature, DeltaH and DeltaS degrees both decrease with an increase in temperature. While the binding is enthalpically favorable at all temperatures studied, at temperatures below 25 degrees C, DeltaG degrees is also favoured by entropic contributions. As the temperature increases, the entropic contributions progressively decrease, attaining a value of zero at 24.3 degrees 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 (DeltaCp degrees ) of -0.238 +/- 0.04 kcal per K per mol of GSH bound.
    European Journal of Biochemistry 09/2001; 268(15):4307-14. · 3.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The binding of three competitive glutathione analogue inhibitors (S-alkylglutathione derivatives) to glutathione S-transferase from Schistosoma japonicum, SjGST, has been investigated by isothermal titration microcalorimetry at pH 6.5 over a temperature range of 15--30 degrees C. Calorimetric measurements in various buffer systems with different ionization heats suggest that no protons are exchanged during the binding of S-alkylglutathione derivatives. Thus, at pH 6.5, the protons released during the binding of substrate may be from its thiol group. Calorimetric analyses show that S-methyl-, S-butyl-, and S-octylglutathione bind to two equal and independent sites in the dimer of SjGST. The affinity of these inhibitors to SjGST is greater as the number of methylene groups in the hydrocarbon side chain increases. In all cases studied, Delta G(0) remains invariant as a function of temperature, while Delta H(b) and Delta S(0) both decrease as the temperature increases. The binding of three S-alkylglutathione derivatives to the enzyme is enthalpically favourable at all temperatures studied. The temperature dependence of the enthalpy change yields negative heat capacity changes, which become less negative as the length of the side chain increases.
    Biochimica et Biophysica Acta 08/2001; 1548(1):106-13. · 4.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The binding of three competitive glutathione analogue inhibitors (S-alkylglutathione derivatives) to glutathione S-transferase from Schistosoma japonicum, SjGST, has been investigated by isothermal titration microcalorimetry at pH 6.5 over a temperature range of 15–30°C. Calorimetric measurements in various buffer systems with different ionization heats suggest that no protons are exchanged during the binding of S-alkylglutathione derivatives. Thus, at pH 6.5, the protons released during the binding of substrate may be from its thiol group. Calorimetric analyses show that S-methyl-, S-butyl-, and S-octylglutathione bind to two equal and independent sites in the dimer of SjGST. The affinity of these inhibitors to SjGST is greater as the number of methylene groups in the hydrocarbon side chain increases. In all cases studied, ΔG0 remains invariant as a function of temperature, while ΔHb and ΔS0 both decrease as the temperature increases. The binding of three S-alkylglutathione derivatives to the enzyme is enthalpically favourable at all temperatures studied. The temperature dependence of the enthalpy change yields negative heat capacity changes, which become less negative as the length of the side chain increases.
    Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 01/2001;