Effect of glutathione, glutathione sulphonate and S-hexylglutathione on the conformational stability of class pi glutathione S-transferase.
The glutathione S-transferases (GST) are a supergene family of phase II detoxification enzymes which catalyse the S-conjugation between glutathione and an electrophilic substrate. The active site can be divided into two adjacent functional regions, a highly specific G-site for binding the physiological substrate glutathione and a nonspecific H-site for binding nonpolar electrophilic substrates. Equilibrium and kinetic unfolding experiments employing tryptophan fluorescence and enzyme activity measurements were preformed to study the effect of ligand binding to the G-site on the unfolding and stability of the porcine class pi glutathione S-transferase against urea. The presence of glutathione caused a shift in the equilibrium-unfolding curves towards lower urea concentrations and enhanced the first-order rate constant for unfolding suggesting a destabilisation of the pGSTP1-1 structure against urea. The presence of either glutathione sulphonate or S-hexylglutathione, however, produced the opposite effect in that their binding to the G-site appeared to exet a stablising effect against urea. The binding of these glutathione analogues also reduced significantly the degree of cooperativity of unfolding indicating a possible change in the protein's unfolding pathway.
Erhardt
J
J
Department of Biochemistry, University of the Witwatersrand, Johanesburg, South Africa.
Dirr
H
H
D000818:Animals; D001665:Binding Sites; D004795:Enzyme Stability; D005978:Glutathione / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005982:Glutathione Transferase / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008168:Lung / Q000201:enzymology; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013552:Swine
C040136:glutathione sulfonate; D005982:Glutathione Transferase; D005978:Glutathione; C033550:hexylglutathione