Kinetic study on the irreversible thermal denaturation of Schistosoma japonicum glutathione S-transferase.
The thermal unfolding pathway of the Schistosoma japonicum glutathione S-transferase (Sj26GST) was previously interpreted by applying equilibrium thermodynamics and a reversible two-state model (Kaplan et al., (1997) Protein Science, 6, 399-406), though weak support for this interpretation was provided. In our study, thermal denaturation of Sj26GST has been re-examined by differential scanning calorimetry in the pH range of 6.5-8.5 and in the presence of the substrate and S-hexylglutathione. Calorimetric traces were found to be irreversible and highly scan-rate dependent. Thermogram shapes, as well as their scan-rate dependence, can be globally explained by assuming that thermal denaturation takes place according to one irreversible step described by a first-order kinetic constant that changes with temperature, as given by an Arrhenius equation. On the basis of this model, values for the rate constant as a function of temperature and the activation energy have been determined. Data also indicate that binding of GSH or S-hexylglutathione just exert a very little stabilising effect on the dimeric structure of the molecule.
Quesada-Soriano
Indalecio
I
Dpto. de Química Física, Bioquímica y Q. Inorgánica, Facultad de Ciencias Experimentales, Universidad de Almería, La Cañada de San Urbano, 04120 Almería, Spain.
García-Maroto
Federico
F
García-Fuentes
Luis
L
D000818:Animals; D002152:Calorimetry, Differential Scanning; D005982:Glutathione Transferase / Q000737:chemistry*; D015801:Helminth Proteins / Q000737:chemistry; D006358:Hot Temperature; D007700:Kinetics; D011489:Protein Denaturation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry; D012549:Schistosoma japonicum / Q000201:enzymology*
D015801:Helminth Proteins; D011994:Recombinant Proteins; D005982:Glutathione Transferase