Inhibition of cytosolic glutathione S-transferase activity from rat liver by copper

Abstract

H2O2 inactivation of particular GST isoforms has been reported, with no information regarding the overall effect of other ROS on cytosolic GST activity. The present work describes the inactivation of total cytosolic GST activity from liver rats by the oxygen radical-generating system Cu2+/ascorbate. We have previously shown that this system may change some enzymatic activities of thiol proteins through two mechanisms: ROS-induced oxidation and non-specific Cu2+ binding to protein thiol groups. In the present study, we show that nanomolar Cu2+ in the absence of ascorbate did not modify total cytosolic GST activity; the same concentrations of Cu2(+) in the presence of ascorbate, however, inhibited this activity. Micromolar Cu2+ in either the absence or presence of ascorbate inhibited cytosolic GST activity. Kinetic studies show that GSH but no 1-chloro-2,4-dinitrobenzene prevent the inhibition on cytosolic GST induced by micromolar Cu2+ either in the absence or presence of ascorbate. On the other hand, NEM and mersalyl acid, both thiol-alkylating agents, inhibited GST activity with differential reactivity in a dose-dependent manner. Taken together, these results suggest that an inhibitory Cu2+-binding effect is likely to be negligible on the overall inhibition of cytosolic GST activity observed by the Cu2+/ascorbate system. We discuss how modification of GST-thiol groups is related to the inhibition of cytosolic GST activity.