RESPONSES OF GLUTATHIONE-RELATED ENZYMES IN ISOLATED RAT SMALL-INTESTINE TO FE2-EDTA-MEDIATED OXIDATIVE STRESS()

The activities of glutathione-related enzymes in isolated rat small in testine were investigated under oxidative stress mediated by Fe2+-EDTA . The isoelectric points and approximate molecular weights of the enzy mes investigated were first determined. The reduced and oxidized gluta thione contents, and low molecular weight thiols in isolated rat small intestine were also studied under oxidative stress. Significant reduc ing activities of glutathione S-transferase and lactate dehydrogenase were observed accompanied by increases in oxidized glutathione content , whereas thioltransferase, glutathione reductase, glutathione peroxid ase and thioredoxin reductase retained the same levels of activity as controls. First-order inactivation of purified rat small intestine glu tathione S-transferase including class-alpha, mu and pi was observed a nd the isozyme class-pi was inactivated at several pH's under Fe2+-EDT A-mediated oxidative stress. Leakage of protein and both reduced and o xidized forms of glutathione was significantly increased during incuba tion with Fe2+-EDTA. In conclusion, enzymes which were not inactivated under Fe2+-EDTA-mediated oxidative stress may play an important role in cellular antioxidant defenses in the small intestine. Furthermore, enzymes such as glutathione S-transferase, mainly a class-pi isozyme, and lactate dehydrogenase which were inactivated may form part of the barrier against oxidative stress similar to reduced glutathione.