Abstract
The effect of enzymatically generated reduced oxygen metabolites on the activity of hepatic microsomal glutathione S-transferase activity was studied to explore possible physiological regulatory mechanisms of the enzyme. Noradrenaline and the microsomal cytochrome P-450-dependent monooxygenase system were used to generate reduced oxygen species. When noradrenaline (greater than 0.1 mM) was incubated with rat liver microsomes in phosphate buffer (pH 7.4), an increase in microsomal glutathione S-transferase activity was observed, and this activation was potentiated in the presence of a NADPH-generating system; the glutathione S-transferase activity was increased to 180% of the control with 1 mM noradrenaline and to 400% with both noradrenaline and NADPH. Superoxide dismutase and catalase inhibited partially the noradrenaline-dependent activation of the enzyme. In the presence of dithiothreitol and glutathione, the activation of the glutathione S-transferase by noradrenaline, with or without NADPH, was not observed. In addition, the activation of glutathione S-transferase activity by noradrenaline and glutathione disulfide was not additive when both compounds were incubated together. These results indicate that the microsomal glutathione S-transferase is activated by reduced oxygen species, such as superoxide anion and hydrogen peroxide. Thus, metabolic processes that generate high concentrations of reduced oxygen species may activate the microsomal glutathione S-transferase, presumably by the oxidation of the sulfhydryl group of the enzyme, and this increased catalytic activity may help protect cells from oxidant-induced damage.
Highlights
Observed, and this activation was potentiated in the reportedthattheglutathione-depletingagentphoroneinpresence of a NADPH-generating system; the glutathi- creases both protein-mixed disulfide formation and microsoone S-transferase activity was increased to 180%of mal glutathione S-transferaseactivity
Noradrenaline, catalase, superoxide dismutase, NADP’, NADPH, glucose 6-phosphate, glutathione, and glutathiondeisulfide were purchased from Sigma. l-Chloro-2,4-dinitrobenzenewas obtained from Wako Pure Chemical Industries, Ltd., Tokyo.Glucose-6-phosphate dehydrogenase was purchased from Oriental Yeast Ltd., Tokyo
Iwt as demonstrated thatliver microthreitol or glutathione (TablesI and 11).These results indicate somal glutathione S-transferase activity is stimulatbeyd northat the noradrenaline-dependent activation of microsomal adrenalinewith or without a NADPH-generatingsystem. glutathione S-transferase activity is due to oxidation of the Much evidence has accumulatedshowing that adrenaline and noradrenalinegenerate reduced oxygen metabolitesduring sulfhydryl groupof the microsomal glutathione S-transferase, their oxidation [19,20,21,22, 25]
Summary
In the presence aobrsence of a NADPH-generating system, glutathioneS-transferase activity. Microsomalglutathione S-trans- Noradrenaline (1 mM) intheabsenceorpresence of a ferase activity was increased 132% by noradrenaline alone, NADPH-generating system increasemdicrosomal glutathione. 260% by a NADPH-generatingsystem,and 400% by the S-transferase activity by about 190 and 400%, respectively, combination of both noradrenaline anad NADPH-generating and this stimulation was reversed by the addition of dithio-. Microsomes were incubated at 37 “C for 10 min in the absence or presence of noradrenaline (1 mM), a NADPH-generatingsystem (NADPH),or dithiothreitol (DTT, 10 mM) as indicated in the table. Transferase activity (GST) was measured as described under “Materials and Methods.” Eachvalue represents the mean f S.D. of two or three incubations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
