title: Glutathione peroxidase protects against peroxynitrite-mediated oxidations. A new function for selenoproteins as peroxynitrite reductase.
abstract: There is a requirement for cellular defense against excessive peroxynitrite generation to protect against DNA strand breaks and mutations and against interference with protein tyrosine-based signaling and other protein functions due to formation of 3-nitrotyrosine. Here, we demonstrate a role of selenium-containing enzymes catalyzing peroxynitrite reduction using glutathione peroxidase (GPx) as an example. GPx protected against the oxidation of dihydrorhodamine 123 by peroxynitrite more effectively than ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a selenoorganic compound exhibiting a high second-order rate constant for the reaction with peroxynitrite, 2 x 10(6) M-1 s-1. Carboxymethylation of selenocysteine in GPx by iodoacetate led to the loss of "classical" glutathione peroxidase activity but maintained protection against peroxynitrite-mediated oxidation. The maintenance of protection by GPx against peroxynitrite requires GSH as reductant. When peroxynitrite was infused to maintain a 0.2 microM steady-state concentration, GPx in the presence of GSH, but neither GPx nor GSH alone, effectively inhibited the hydroxylation of benzoate by peroxynitrite. Under these steady-state conditions peroxynitrite did not cause the loss of classical GPx activity. GPx, like selenomethionine, protected against protein 3-nitrotyrosine formation in human fibroblast lysates, shown in Western blots. The formation of nitrite rather than nitrate from peroxynitrite was enhanced by GPx or by selenomethionine. The results demonstrate a novel function of GPx and potentially of other selenoproteins containing selenocysteine or selenomethionine, in the GSH-dependent maintenance of a defense line against peroxynitrite-mediated oxidations, as a peroxynitrite reductase.
authors.affiliation: Institut für Physiologische Chemie I, Heinrich-Heine-Universität Düsseldorf, Postfach 101007, D-40001 Düsseldorf, Germany. helmut.sies@uni-duesseldorf.de
authors.forename: H
authors.initials: H
authors.lastname: Sies
authors.forename: V S
authors.initials: VS
authors.lastname: Sharov
authors.forename: L O
authors.initials: LO
authors.lastname: Klotz
authors.forename: K
authors.initials: K
authors.lastname: Briviba
mesh_terms: D001393:Azoles / Q000494:pharmacology; D001565:Benzoates / Q000378:metabolism; D019817:Benzoic Acid; D005979:Glutathione Peroxidase / Q000502:physiology*; D006801:Humans; D006900:Hydroxylation; D054833:Isoindoles; D009566:Nitrates / Q000494:pharmacology*; D016566:Organoselenium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000502:physiology*; D011506:Proteins / Q000502:physiology*; D051140:Selenoproteins
chemical_list: D001393:Azoles; D001565:Benzoates; D054833:Isoindoles; D009566:Nitrates; D016566:Organoselenium Compounds; D011506:Proteins; D051140:Selenoproteins; C039642:peroxynitric acid; C042986:ebselen; D019817:Benzoic Acid; D010088:Oxidoreductases; D005979:Glutathione Peroxidase; C109110:peroxynitrite reductase