Radical production from free and peptide-bound methionine sulfoxide oxidation by peroxynitrite and hydrogen peroxide/iron(II)

Methionine sulfoxide is a post-translational protein modification that has been receiving increasing attention in the literature. Here we used electron paramagnetic resonance spin trapping techniques to show that free and peptide-bound methionine sulfoxide is oxidized by hydrogen peroxide/iron(II)-EDTA and peroxynitrite through the intermediacy of the hydroxyl radical to produce both (CH3)-C-. and (CH2CH2CH)-C-. radicals. The results indicate that methionine sulfoxide residues are important targets of reactive oxygen- and nitrogen-derived species in proteins. Since the produced protein-derived radicals can propagate oxidative damage, the results add a new antioxidant route for the action of the enzyme peptide methionine sulfoxide reductase. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.