Background: Tyrosyl radicals react with superoxide to form bicyclic hydroperoxides that contains an ␣-␤ unsaturated carbonyl. Results: GSH undergoes Michael addition with Tyr hydroperoxides in peptides and myoglobin. Conclusion: Proteins that form hydroperoxides through radical-mediated oxidation should readily form GSH-Tyr adducts. Significance: This is a novel mechanism of protein-glutathione adduct formation, and similar chemistry could result in Cys-Tyr cross-linking of proteins during oxidative stress.

PAGE 26075:Fig. 6 has been revised to correct an error in the quantification of GSH adducts. The data points in the original Fig. 6A were mistakenly calculated for only one of the major GSH adduct peaks (shown in Fig. 4B), giving a false impression of a lag between substrate loss and product formation. This is not the case when all product peaks are integrated (as they do not decay at the same rate). The corrected figure shows integration for all of the peaks. The open circles in Fig. 6B were at zero on the y axis and indicated that no product was formed when the reduced GSH adduct was incubated over time. The data correspond to the open circles in Fig. 6A showing no loss of starting material. Rather than showing the zero points, the legend has been revised to indicate that no reduced hydroxide was detected in the sample reduced with NaBH 4 . These corrections do not affect the interpretation of the results or the conclusions of this work.