RT Journal Article SR Electronic T1 Activation of Microsomal Glutathione S-Transferase by Peroxynitrite JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 136 OP 146 DO 10.1124/mol.63.1.136 VO 63 IS 1 A1 Yanbin Ji A1 Brian M. Bennett YR 2003 UL http://molpharm.aspetjournals.org/content/63/1/136.abstract AB Peroxynitrite (ONOO−) toxicity is associated with protein oxidation and/or tyrosine nitration, usually resulting in inhibition of enzyme activity. We examined the effect of ONOO− on the activity of purified rat liver microsomal glutathioneS-transferase (GST) and found that the activity of reduced glutathione (GSH)-free enzyme was increased 4- to 5-fold by 2 mM ONOO−; only 15% of this increased activity was reversed by dithiothreitol. Exposure of the microsomal GST to ONOO− resulted in concentration-dependent oxidation of protein sulfhydryl groups, dimer and trimer formation, protein fragmentation, and tyrosine nitration. With the exception of sulfhydryl oxidation, these modifications of the enzyme correlated well with the increase in enzyme activity. Nitration or acetylation of tyrosine residues of the enzyme using tetranitromethane andN-acetylimidazole, respectively, also resulted in increased enzyme activity, providing additional evidence that modification of tyrosine residues can alter catalytic activity. Addition of ONOO−-treated microsomal GST to microsomal membrane preparations caused a marked reduction in iron-induced lipid peroxidation, which raises the possibility that this enzyme may act to lessen the degree of membrane damage that would otherwise occur under pathophysiological conditions of increased ONOO−formation.