title: The high non-enzymatic conjugation rates of some glutathione S-transferase (GST) substrates at high glutathione concentrations.
abstract: Enzymatic properties of five human glutathione S-transferases (GSTs) and non-enzymatic conjugation rates of GST substrates were examined as a function of glutathione (GSH) concentration and pH. GSTP1-1 showed a broad substrate specificity with both low and high GSH (10 mM) concentrations at pH 7.0, and the inhibitor insensitivity was then prominent. Among the GST substrates tested, ethacrynic acid, p-nitrophenylacetate, 1-chloro-2,4-dinitrobenzene and trans-4-phenyl-3-buten-2-one conjugated nonenzymatically with half-times of 0.39, 3.1, 9.4 and 10.0 min respectively at 10 mM GSH, pH 7.0 and 35 degrees C. The half-time for acrolein estimated by extrapolation was approximately 0.5 s. While the enzymatic reaction rates were independent of GSH at concentrations larger than Km values according to Michaelis-Menten kinetics and relatively insensitive to a pH change from 6.5 to 7.0, the non-enzymatic ones were linearly proportional to the GSH concentration and sensitive to pH. The enhanced non-enzymatic conjugation of various electrophiles at high GSH concentrations may in part account for the physiological significance of GSH elevation in preneoplastic and neoplastic cells.
authors.affiliation: Second Department of Biochemistry, Hirosaki University, School of Medicine, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Satoh
mesh_terms: D005260:Female; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D012680:Sensitivity and Specificity; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D007527:Isoenzymes; D005982:Glutathione Transferase; D005978:Glutathione