Carbon Dioxide Stimulates the Production of Thiyl, Sulfinyl, and Disulfide Radical Anion from Thiol Oxidation by Peroxynitrite

Abstract

Reaction of peroxynitrite with the biological ubiquitous CO 2 produces about 35% yields of two relatively strong one-electron oxidants, CO 3 . and ⅐ NO 2 , but the remaining of peroxynitrite is isomerized to the innocuous nitrate. Partial oxidant deactivation may confound interpretation of the effects of HCO 3 ؊ /CO 2 on the oxidation of targets that react with peroxynitrite by both one-and two-electron mechanisms. Thiols are example of such targets, and previous studies have reported that HCO 3 ؊ / CO 2 partially inhibits GSH oxidation by peroxynitrite at pH 7.4. To differentiate the effects of HCO 3 ؊ /CO 2 on twoand one-electron thiol oxidation, we monitored GSH, cysteine, and albumin oxidation by peroxynitrite at pH 5.4 and 7.4 by thiol disappearance, oxygen consumption, fast flow EPR, and EPR spin trapping. Our results demonstrate that HCO 3 ؊ /CO 2 diverts thiol oxidation by peroxynitrite from two-to one-electron mechanisms particularly at neutral pH. At acid pH values, thiol oxidation to free radicals predominates even in the absence of HCO 3 ؊ /CO 2 . In addition to the previously characterized thiyl radicals (RS ⅐ ), we also characterized radicals derived from them such as the corresponding sulfinyl (RSO ⅐ ) and disulfide anion radical (RSSR ⅐ ؊ ) of both GSH and cysteine. Thiyl, RSO ⅐ and RSSR ⅐ ؊ are reactive radicals that may contribute to the biodamaging and bioregulatory actions of peroxynitrite.Peroxynitrite 1 (ONOO Ϫ ϩ ONOOH), which is formed by the fast reaction between ⅐ NO and O 2 . , has been receiving increasing attention as a mediator of human diseases and as a toxin against invading microorganisms (1-5). The compound is a potent oxidant that is able to oxidize and nitrate a variety of biological targets by mechanisms that are presently being elucidated (6 -16). In general terms, peroxynitrite-mediated oxidations are either bimolecular, first order on peroxynitrite and biomolecule concentration, or unimolecular, first order on peroxynitrite and independent of biomolecule concentration. Bimolecular processes can result in product yield either around stoichiometry and over, as is the case for thiol oxidation (17), or around 35% , as is the case for carbon dioxide (CO 2 ) oxidation (10, 14 -16). Presently, most investigators accept that product yields around 30% are characteristic of peroxynitrite-mediated free radical processes. Indeed, it has been established that ONOO Ϫ protonation (pK a ϭ 6.6) leads to its fast decomposition (k ϭ 0.17 s Ϫ1 at pH 7.4) to yield approximately 70% nitrate and 30% hydroxyl radical ( ⅐ OH) and nitrogen dioxide ( ⅐ NO 2 ) (Fig. 1, path 1) (7)(8)(9)(11)(12)(13)(14). These radicals are the species responsible for peroxynitrite-mediated unimolecular oxidations. In the presence of HCO 3 Ϫ , ONOO Ϫ decomposes much faster because of its reaction with CO 2 (k ϭ 2.6 ϫ 10 4 M Ϫ1 s Ϫ1 at pH 7.4, 25°C) (18, 19) to produce approximately 65% nitrate and 35% carbonate radical anion (CO 3 . ) and ⅐ NO 2 (Fig. 1, path 2) (10, 14 -16).The fast rate constant of this reaction and...

Production of the Carbonate Radical Anion during Xanthine Oxidase Turnover in the Presence of Bicarbonate

“…9 and 10) except for direct EPR (19). The use of the latter was precluded by the low flux of produced radicals (55). The similar emission spectra obtained with XO incubations and flow mixtures of peroxynitrite with the bicarbonate-carbon dioxide pair (Fig.…”

Involvement of inducible nitric oxide synthase in hydroxyl radical-mediated lipid peroxidation in streptozotocin-induced diabetes

“…Under these circumstances, other nitric oxide synthases have previously been shown to produce • NO and O 2 • − simultaneously, leading to peroxynitrite production [42;46;47], which is a transition metal-independent source of • OH [48][49][50][51][52]. Although peroxynitrite homolysis to • OH is expected to be a minor route in vivo, such a reaction may acquire significant relevance in hydrophobic environments and initiate lipid peroxidation [53].…”

Detection, Quantitation, Purification, and Identification of Cardiac Proteins S-Thiolated during Ischemia and Reperfusion

“…It is likely that S-thiolation occurs at the reactive and catalytically essential cysteine 149 (34). Oxidation of this residue inactivates the enzyme and may be achieved by a range of oxidants including GSSG, GSNO, NO, HOCl, and GS(O)SG (33,(35)(36)(37)(38)(39)(40). Triosephosphate isomerase is another glycolytic enzyme that we found to be S-thiolated during cardiac oxidative stress.…”