Inactivation of antioxidant enzymes by peroxynitrite

Exposure of hemolysates and whole erythrocytes to peroxynitrite (bolus of 50 micromol dm(-3)-2 mmol dm(-3)) was found to inactivate erythrocyte antioxidant enzymes: glutathione peroxidase > superoxide dismutase > catalase. Inactivation of antioxidant enzymes by peroxynitrite may be one reason for the secondary oxidative stress in peroxynitrite-treated cells. When hemoglobin was not converted into the cyanmet form, an apparent activation of glutathione peroxidase activity by peroxynitrite was observed in hemolysates; this effect was artifactual and due to the pseudoenzymatic glutathione peroxidase activity of hemoglobin.