Peroxynitrite, a Stealthy Biological Oxidant
2013; Elsevier BV; Volume: 288; Issue: 37 Linguagem: Inglês
10.1074/jbc.r113.472936
ISSN1083-351X
Autores Tópico(s)Vanadium and Halogenation Chemistry
ResumoPeroxynitrite is the product of the diffusion-controlled reaction of nitric oxide and superoxide radicals. Peroxynitrite, a reactive short-lived peroxide with a pKa of 6.8, is a good oxidant and nucleophile. It also yields secondary free radical intermediates such as nitrogen dioxide and carbonate radicals. Much of nitric oxide- and superoxide-dependent cytotoxicity resides on peroxynitrite, which affects mitochondrial function and triggers cell death via oxidation and nitration reactions. Peroxynitrite is an endogenous toxicant but is also a cytotoxic effector against invading pathogens. The biological chemistry of peroxynitrite is modulated by endogenous antioxidant mechanisms and neutralized by synthetic compounds with peroxynitrite-scavenging capacity. Peroxynitrite is the product of the diffusion-controlled reaction of nitric oxide and superoxide radicals. Peroxynitrite, a reactive short-lived peroxide with a pKa of 6.8, is a good oxidant and nucleophile. It also yields secondary free radical intermediates such as nitrogen dioxide and carbonate radicals. Much of nitric oxide- and superoxide-dependent cytotoxicity resides on peroxynitrite, which affects mitochondrial function and triggers cell death via oxidation and nitration reactions. Peroxynitrite is an endogenous toxicant but is also a cytotoxic effector against invading pathogens. The biological chemistry of peroxynitrite is modulated by endogenous antioxidant mechanisms and neutralized by synthetic compounds with peroxynitrite-scavenging capacity. Free radicals typically react fast with each other via radical-radical coupling reactions. Indeed, radical combination reactions usually occur at near diffusion-controlled rates (1Ross W.G.M. Helman W.P. Buxton G.V. Huie R.E. Neta P. NDRL/NIST Solution Kinetics Database. National Institute of Standards and Technology, Gaithersburg, MD1995Google Scholar). This unique type of reaction is, in many cases, kinetically and thermodynamically favored by the fact that it results in the formation of a new chemical bond at the expense of the unpaired electrons of the precursors. There are many possible radical-radical combination reactions that can happen biologically, but low steady-state levels of intermediates and competing reactions usually limit reaction yields and quantitative relevance. A prime example of a relevant radical species produced at high rates biologically is represented by the superoxide radical anion (O2⨪), the product of the univalent reduction of molecular oxygen (2Fridovich I. Superoxide radical and superoxide dismutases.Annu. Rev. Biochem. 1995; 64: 97-112Crossref PubMed Scopus (2720) Google Scholar). O2⨪ is ubiquitous and continuously formed during normal cellular metabolism, with its production rates increasing severalfold during the disruption of cellular redox homeostasis and with inflammatory stimuli. Although excess O2⨪ production has been associated with oxidative damage, more controlled fluxes can lead to redox signaling (3Sies H. Jones D.P. Oxidative stress.in: Fink G. 2nd Ed. Encyclopedia of Stress. 3. Elsevier/Academic Press, London2007: 45-48Crossref Google Scholar). The discovery of nitric oxide (•NO) as an enzymatically generated free radical was paralleled by the recognition that it could readily react with O2⨪ (4Gryglewski R.J. Palmer R.M. Moncada S. Superoxide anion is involved in the breakdown of endothelium-derived vascular relaxing factor.Nature. 1986; 320: 454-456Crossref PubMed Scopus (2183) Google Scholar, 5Ignarro L.J. Byrns R.E. Buga G.M. Wood K.S. Chaudhuri G. Pharmacological evidence that endothelium-derived relaxing factor is nitric oxide: use of pyrogallol and superoxide dismutase to study endothelium-dependent and nitric oxide-elicited vascular smooth muscle relaxation.J. Pharmacol. Exp. Ther. 1988; 244: 181-189PubMed Google Scholar). •NO produced by a variety of nitric-oxide synthases (NOS) 2The abbreviations used are: NOS, nitric-oxide synthase(s); SOD, superoxide dismutase(s); MnP, Mn-porphyrin(s). participates as a mediator in the regulation of vascular tone, neurotransmission, and immunity, among other metabolic and cell signaling effects (6Bredt D.S. Snyder S.H. Nitric oxide: a physiologic messenger molecule.Annu. Rev. Biochem. 1994; 63: 175-195Crossref PubMed Scopus (2132) Google Scholar, 7Hill B.G. Dranka B.P. Bailey S.M. Lancaster Jr., J.R. Darley-Usmar V.M. What part of NO don't you understand? Some answers to the cardinal questions in nitric oxide biology.J. Biol. Chem. 2010; 285: 19699-19704Abstract Full Text Full Text PDF PubMed Scopus (247) Google Scholar). Thus, the reaction of O2⨪ with •NO was first conceived as a mechanism of •NO “inactivation” (8Ignarro L.J. Biosynthesis and metabolism of endothelium-derived nitric oxide.Annu. Rev. Pharmacol. Toxicol. 1990; 30: 535-560Crossref PubMed Scopus (1222) Google Scholar). Notably, the combination reaction leads to peroxynitrite (9Blough N.V. Zafiriou O.C. Reaction of superoxide with nitric oxide to form peroxonitrite in alkaline aqueous solution.Inorg. Chem. 1985; 24: 3502-3504Crossref Scopus (430) Google Scholar, 10Beckman J.S. Beckman T.W. Chen J. Marshall P.A. Freeman B.A. Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide.Proc. Natl. Acad. Sci. U.S.A. 1990; 87: 1620-1624Crossref PubMed Scopus (6698) Google Scholar), a peroxy acid originally studied in the chemical literature as a strong oxidizing and nitrating compound (11Halfpenny E. Robinson P.L. The nitration and hydroxylation of aromatic compounds by pernitrous acid.J. Chem. Soc. 1952; : 939-946Crossref Scopus (98) Google Scholar, 12Mahoney L.R. Evidence for the formation of hydroxyl radicals in the isomerization of pernitrous acid to nitric acid in aqueous solution.J. Am. Chem. Soc. 1970; 92: 5262-5263Crossref Scopus (93) Google Scholar) (Equation 1). O2⋅−+·NO→ONOO−(Eq. 1) The reaction of •NO with O2⨪ occurs biologically even in the presence of superoxide dismutase (SOD), indicating that it is extremely fast to outcompete the enzyme-catalyzed dismutation (Equation 2). O2⋅−+O2⋅−+2H+SOD→ H2O2+O2(Eq. 2) Indeed, the formation of peroxynitrite occurs with a k1 of ∼1010 m−1 s−1, ∼1 order of magnitude higher than that of enzymatic dismutation (∼1–2 × 109 m−1 s−1) (2Fridovich I. Superoxide radical and superoxide dismutases.Annu. Rev. Biochem. 1995; 64: 97-112Crossref PubMed Scopus (2720) Google Scholar, 13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar). Although SOD exists in cells in micromolar levels, •NO concentrations can, in some cases, reach close to micromolar values. Thus, under appropriate conditions, the formation of peroxynitrite is the only known reaction for O2⨪ in biology that can be similar or even substantially faster than the dismutation reaction (i.e. Equation 3). k1×[·NO][O2−·]≥k2+[SOD][O2−·]⇒k1×[·NO]≥k2×[SOD](Eq. 3) Although the proximal species formed from the •NO plus O2⨪ reaction is peroxynitrite anion, the pKa value of 6.8 and the rapid protonation imply that, under most biological conditions, ONOO− and ONOOH will both be present (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar) (Equation 4). ONOO-+H+⇌ONOOH(Eq. 4) For instance, at pH 7.4, ∼80% of peroxynitrite will be in the anionic form; conversely, at pH 6.2 (e.g. inside a macrophage phagocytic vacuole), up to 80% will be in the protonated form. The stability, reactivity, and capacity to permeate membranes of ONOO− and ONOOH are quite different (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar, 14Denicola A. Souza J.M. Radi R. Diffusion of peroxynitrite across erythrocyte membranes.Proc. Natl. Acad. Sci. U.S.A. 1998; 95: 3566-3571Crossref PubMed Scopus (365) Google Scholar), and therefore, the biochemistry of peroxynitrite in biological systems is highly pH-dependent. This acid-base property of peroxynitrite contrasts with that of H2O2, which has a pKa of ∼11.6 and therefore is almost 100% protonated in the physiological pH range. As peroxide, the relatively labile O–O bond provides the possibility of homolysis to radicals (10Beckman J.S. Beckman T.W. Chen J. Marshall P.A. Freeman B.A. Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide.Proc. Natl. Acad. Sci. U.S.A. 1990; 87: 1620-1624Crossref PubMed Scopus (6698) Google Scholar, 12Mahoney L.R. Evidence for the formation of hydroxyl radicals in the isomerization of pernitrous acid to nitric acid in aqueous solution.J. Am. Chem. Soc. 1970; 92: 5262-5263Crossref Scopus (93) Google Scholar, 15Augusto O. Gatti R.M. Radi R. Spin-trapping studies of peroxynitrite decomposition and of 3-morpholinosydnonimine N-ethylcarbamide autooxidation: direct evidence for metal-independent formation of free radical intermediates.Arch. Biochem. Biophys. 1994; 310: 118-125Crossref PubMed Scopus (168) Google Scholar, 16Goldstein S. Merényi G. The chemistry of peroxynitrite: implications for biological activity.Methods Enzymol. 2008; 436: 49-61Crossref PubMed Scopus (120) Google Scholar). Indeed, protonation weakens the O–O bond in ONOOH and leads to homolytic cleavage to hydroxyl radicals (•OH) and nitrogen dioxide (•NO2), two strongly oxidizing/hydroxylating and nitrating species, respectively (Equation 5). ONOOH+·NO2+·OH(Eq. 5) The homolytic cleavage occurs with a k4 of 4.5 s−1 at 37 °C, resulting in a half-life of 0.8 s in phosphate buffer at pH 7.4 (i.e. kapp = 0.9 s−1) (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar). The recognition that the homolysis of ONOOH could yield •OH led to the postulation of a new biologically relevant mechanism of oxygen radical-mediated molecular damage, without the requirement of transition metal-dependent reactions. Indeed, until the emergence of peroxynitrite, much of O2⨪-dependent oxidative damage was postulated to occur via the Haber-Weiss cycle and/or the Fenton reaction (2Fridovich I. Superoxide radical and superoxide dismutases.Annu. Rev. Biochem. 1995; 64: 97-112Crossref PubMed Scopus (2720) Google Scholar), where ultimately •OH was formed (Equation 6). H2O2+Fe2+→·OH + OH−+Fe3+(Eq. 6) In fact, O2⨪ is not a strong oxidant, and actually, it can also act as a reductant (17Buettner G.R. The pecking order of free radicals and antioxidants: lipid peroxidation, α-tocopherol, and ascorbate.Arch. Biochem. Biophys. 1993; 300: 535-543Crossref PubMed Scopus (2058) Google Scholar). Therefore, its direct toxicity is usually limited (i.e. oxidation and disruption of the iron-sulfur cluster in [4Fe-4S]-containing dehydratases) (2Fridovich I. Superoxide radical and superoxide dismutases.Annu. Rev. Biochem. 1995; 64: 97-112Crossref PubMed Scopus (2720) Google Scholar). Moreover, despite high formation rates (18Winterbourn C.C. Hampton M.B. Livesey J.H. Kettle A.J. Modeling the reactions of superoxide and myeloperoxidase in the neutrophil phagosome. Implications for microbial killing.J. Biol. Chem. 2006; 281: 39860-39869Abstract Full Text Full Text PDF PubMed Scopus (497) Google Scholar), the steady-state levels of O2⨪ are always quite low due to the abundance and thorough distribution of SOD that promote its preferential dismutation to H2O2 (unless •NO is present). Thus, considerable O2⨪-dependent toxicity resides in the formation of secondary reactive species; these include H2O2 (Equation 6), peroxynitrite (Equation 1; to be analyzed in this minireview), and, possibly, reactive hydroperoxides formed by the fast reactions of O2⨪ with biomolecule-derived radicals (19Winterbourn C.C. Parsons-Mair H.N. Gebicki S. Gebicki J.M. Davies M.J. Requirements for superoxide-dependent tyrosine hydroperoxide formation in peptides.Biochem. J. 2004; 381: 241-248Crossref PubMed Scopus (91) Google Scholar, 20Möller M.N. Hatch D.M. Kim H.Y. Porter N.A. Superoxide reaction with tyrosyl radicals generates para-hydroperoxy and para-hydroxy derivatives of tyrosine.J. Am. Chem. Soc. 2012; 134: 16773-16780Crossref PubMed Scopus (36) Google Scholar). Similarly, although •NO was recognized early as a cytotoxic effector during cellular immune responses mediated by macrophages and neutrophils (21Nathan C.F. Hibbs Jr., J.B. Role of nitric oxide synthesis in macrophage antimicrobial activity.Curr. Opin. Immunol. 1991; 3: 65-70Crossref PubMed Scopus (1325) Google Scholar), the biological effects of •NO did not correlate well with its chemical reactivity, i.e. a relatively stable radical with modest redox properties (22Radi R. Reactions of nitric oxide with metalloproteins.Chem. Res. Toxicol. 1996; 9: 828-835Crossref PubMed Scopus (137) Google Scholar). Thus, •NO-mediated toxicity was also further rationalized considering the generation of •NO-derived oxidants (23Radi R. Nitric oxide, oxidants, and protein tyrosine nitration.Proc. Natl. Acad. Sci. U.S.A. 2004; 101: 4003-4008Crossref PubMed Scopus (1215) Google Scholar) such as peroxynitrite. Soon after the proposal of the formation and homolysis of peroxynitrite in biological systems (10Beckman J.S. Beckman T.W. Chen J. Marshall P.A. Freeman B.A. Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide.Proc. Natl. Acad. Sci. U.S.A. 1990; 87: 1620-1624Crossref PubMed Scopus (6698) Google Scholar), it was reported that peroxynitrite could directly oxidize thiol groups at rates much faster than the homolytic cleavage (24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar). Overall, the initial observations (10Beckman J.S. Beckman T.W. Chen J. Marshall P.A. Freeman B.A. Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide.Proc. Natl. Acad. Sci. U.S.A. 1990; 87: 1620-1624Crossref PubMed Scopus (6698) Google Scholar, 24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar, 25Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite-induced membrane lipid peroxidation: the cytotoxic potential of superoxide and nitric oxide.Arch. Biochem. Biophys. 1991; 288: 481-487Crossref PubMed Scopus (2043) Google Scholar) paved the way for a new paradigm of O2⨪- and •NO-mediated toxicity via peroxynitrite, which was schematized in JBC in 1991 (Fig. 1, upper) (24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar). The hypothesis led to predictions that could be tested experimentally, including how the inhibition of nitric oxide synthesis (e.g. using NOS inhibitors), the elimination of excess O2⨪ (e.g. overexpression of SOD), the catalytic decomposition of peroxynitrite, or the scavenging of peroxynitrite-derived radicals could influence oxidative processes and biological outcome. An updated version of the original proposal is shown in Fig. 1 (lower) and is analyzed below. Peroxynitrite is both an oxidant and nucleophile, and these two chemical properties dictate much of its biochemical actions in vivo (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar). First, as an oxidant, it can promote one- and two-electron oxidations by direct reactions with biomolecular targets. Indeed, the redox potentials of peroxynitrite at pH 7 (E′0) for the ONOO−/•NO2 and ONOO−/NO2− pairs have been estimated as 1.4 and 1.2 V, respectively (26Koppenol W.H. Moreno J.J. Pryor W.A. Ischiropoulos H. Beckman J.S. Peroxynitrite, a cloaked oxidant formed by nitric oxide and superoxide.Chem. Res. Toxicol. 1992; 5: 834-842Crossref PubMed Scopus (1278) Google Scholar), supporting its performance as a good biological oxidant from a thermodynamic viewpoint (17Buettner G.R. The pecking order of free radicals and antioxidants: lipid peroxidation, α-tocopherol, and ascorbate.Arch. Biochem. Biophys. 1993; 300: 535-543Crossref PubMed Scopus (2058) Google Scholar). A prime example of two-electron oxidations corresponds to the reaction of peroxynitrite with thiols, which yields the sulfenic acid derivative (and nitrite) (24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar, 27Trujillo M. Radi R. Peroxynitrite reaction with the reduced and the oxidized forms of lipoic acid: new insights into the reaction of peroxynitrite with thiols.Arch. Biochem. Biophys. 2002; 397: 91-98Crossref PubMed Scopus (166) Google Scholar) (Equation 7). ONOOH+RS−→NO2-+RSOH(Eq. 7) This reaction was originally described for cysteine and the single thiol group of albumin (Cys-34) and occurs with an apparent second-order rate constant of >103 m−1 s−1 at pH 7.4 and 37 °C (Table 1), ∼3 orders of magnitude faster than the same reaction with H2O2. These data underscored the high chemical reactivity of peroxynitrite in biological systems (24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar). Nonetheless, peroxynitrite is less reactive toward thiols than other biologically relevant two-electron oxidants such as hypochlorous acid (HOCl) and hypobromous acid (HOBr), which react with cysteine and glutathione on the order of 107 m−1 s−1 (28Peskin A.V. Winterbourn C.C. Kinetics of the reactions of hypochlorous acid and amino acid chloramines with thiols, methionine, and ascorbate.Free Radic. Biol. Med. 2001; 30: 572-579Crossref PubMed Scopus (301) Google Scholar, 29Pattison D.I. Davies M.J. Kinetic analysis of the reactions of hypobromous acid with protein components: implications for cellular damage and use of 3-bromotyrosine as a marker of oxidative stress.Biochemistry. 2004; 43: 4799-4809Crossref PubMed Scopus (167) Google Scholar). The reactivity of peroxynitrite with thiols is intermediary between that of H2O2 and that of hypohalous acids, resulting in a moderately strong and selective biological oxidant in a similar way to what has been proposed for thiol oxidation mediated by chloramines (k ∼ 100–200 m−1 s−1) (28Peskin A.V. Winterbourn C.C. Kinetics of the reactions of hypochlorous acid and amino acid chloramines with thiols, methionine, and ascorbate.Free Radic. Biol. Med. 2001; 30: 572-579Crossref PubMed Scopus (301) Google Scholar). Importantly, peroxynitrite can oxidize at even more remarkable rates some “fast reacting thiols,” such as those present in mammalian and microbial peroxiredoxins (30Ferrer-Sueta G. Manta B. Botti H. Radi R. Trujillo M. Denicola A. Factors affecting protein thiol reactivity and specificity in peroxide reduction.Chem. Res. Toxicol. 2011; 24: 434-450Crossref PubMed Scopus (216) Google Scholar). Indeed, peroxiredoxins react with peroxynitrite with constants on the order of 106–107 m−1 s−1 (Table 1) and represent a first line of enzymatic antioxidant defense against peroxynitrite.TABLE 1Kinetic aspects of peroxynitrite-mediated oxidations: selected reactions of biochemical relevanceReactantkaStopped-flow spectrophotometry has been utilized to determine the rate constants of peroxynitrite reaction with most compounds, taking advantage of the distinctive optical absorption of ONOO− at 302 nm (ϵ = 1670 m−1 cm−1) as originally reported (24). Alternative approaches have been also used, with the application of competition kinetics with reference reactions of known rate constants (81).ProcessCommentarym−1s−1Tyrosine0Tyr oxidation and nitrationThere is no direct reaction (40Alvarez B. Ferrer-Sueta G. Freeman B.A. Radi R. Kinetics of peroxynitrite reaction with amino acids and human serum albumin.J. Biol. Chem. 1999; 274: 842-848Abstract Full Text Full Text PDF PubMed Scopus (241) Google Scholar). Tyr oxidation and nitration is accomplished by peroxynitrite-derived radicals (23Radi R. Nitric oxide, oxidants, and protein tyrosine nitration.Proc. Natl. Acad. Sci. U.S.A. 2004; 101: 4003-4008Crossref PubMed Scopus (1215) Google Scholar).Tryptophan40Trp oxidation and nitrationThe direct reaction is rather slow and can cause Trp nitration (96Alvarez B. Rubbo H. Kirk M. Barnes S. Freeman B.A. Radi R. Peroxynitrite-dependent tryptophan nitration.Chem. Res. Toxicol. 1996; 9: 390-396Crossref PubMed Scopus (233) Google Scholar).Methionine360Methionine sulfoxide formationIt can account for enzyme inactivation (97Pryor W.A. Jin X. Squadrito G.L. One- and two-electron oxidations of methionine by peroxynitrite.Proc. Natl. Acad. Sci. U.S.A. 1994; 91: 11173-11177Crossref PubMed Scopus (361) Google Scholar). It is sometimes used to scavenge peroxynitrite in biochemical systems.Uric acid500A variety of oxidation products can be formed, including allantoin, alloxan, and triuret (83Santos C.X. Anjos E.I. Augusto O. Uric acid oxidation by peroxynitrite: multiple reactions, free radical formation, and amplification of lipid oxidation.Arch. Biochem. Biophys. 1999; 372: 285-294Crossref PubMed Scopus (224) Google Scholar, 85Robinson K.M. Morré J.T. Beckman J.S. Triuret: a novel product of peroxynitrite-mediated oxidation of urate.Arch. Biochem. Biophys. 2004; 423: 213-217Crossref PubMed Scopus (58) Google Scholar). The intermediate formation of uric acid-derived radicals may promote secondary oxidation reactions and products such as urate hydroperoxide (83Santos C.X. Anjos E.I. Augusto O. Uric acid oxidation by peroxynitrite: multiple reactions, free radical formation, and amplification of lipid oxidation.Arch. Biochem. Biophys. 1999; 372: 285-294Crossref PubMed Scopus (224) Google Scholar, 98Meotti F.C. Jameson G.N. Turner R. Harwood D.T. Stockwell S. Rees M.D. Thomas S.R. Kettle A.J. Urate as a physiological substrate for myeloperoxidase: implications for hyperuricemia and inflammation.J. Biol. Chem. 2011; 286: 12901-12911Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar).It is good inhibitor of peroxynitrite-dependent processes in vitro and in vivo. The direct reaction is relatively slow, so protection is ascribed to reaction with peroxynitrite-derived radicals. Uric acid is also a physiological substrate of myeloperoxidase (98Meotti F.C. Jameson G.N. Turner R. Harwood D.T. Stockwell S. Rees M.D. Thomas S.R. Kettle A.J. Urate as a physiological substrate for myeloperoxidase: implications for hyperuricemia and inflammation.J. Biol. Chem. 2011; 286: 12901-12911Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar) and may therefore interfere in heme peroxidase-dependent nitration reactions as well.GlutathionebThe actual reactants are peroxynitrous acid and the thiolate anion (Equation 7) (27); thus, the observed apparent reaction rate is strongly pH-dependent (24), with the thiol pKSH representing a relevant variable. The table shows kapp, which is on the order of 103 m−1 s−1; however, the actual (pH-independent) rate constant of the reaction is on the order of 105 m−1 s1 (27, 30).1400It evolves mainly to glutathione disulfide through the intermediacy of glutathione sulfenic acid (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar). Glutathionyl radicals can be formed from peroxynitrite-derived radicals.It is an endogenous compound that decomposes peroxynitrite. Considering a 5 mm intracellular concentration, the k[GSH]cThe product of the second-order rate constant times the concentration of the reactant provides a pseudo-first-order rate constant in s−1 that allows ready comparison of the kinetic biological relevance among different peroxynitrite targets. product results in a value of 7 s−1, significantly faster that the rate constant of homolysis (0.9 s−1)dIn fact, the homolytic yields of •NO2 and •OH are ∼30% of ONOOH due to “in cage” recombination of nascent radicals to nitrate (NO3−) before their diffusion to the bulk aqueous phase. but much less than that of other direct reactions, so its direct reaction with peroxynitrite in biological systems is modest.CysteinebThe actual reactants are peroxynitrous acid and the thiolate anion (Equation 7) (27); thus, the observed apparent reaction rate is strongly pH-dependent (24), with the thiol pKSH representing a relevant variable. The table shows kapp, which is on the order of 103 m−1 s−1; however, the actual (pH-independent) rate constant of the reaction is on the order of 105 m−1 s1 (27, 30).5900It evolves to cysteine disulfide (cystine) through the intermediacy of cysteine sulfenic acid (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar, 24Radi R. Beckman J.S. Bush K.M. Freeman B.A. Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide.J. Biol. Chem. 1991; 266: 4244-4250Abstract Full Text PDF PubMed Google Scholar).This was the first determination of a second-order rate constant of peroxynitrite reaction with a biomolecule. It provided the concept that direct reactions of peroxynitrite may be more relevant in biology than homolysis.Human serum albumin9700About 40% of the direct reactivity is due to the reaction with the single thiol group (Cys-34) (40Alvarez B. Ferrer-Sueta G. Freeman B.A. Radi R. Kinetics of peroxynitrite reaction with amino acids and human serum albumin.J. Biol. Chem. 1999; 274: 842-848Abstract Full Text Full Text PDF PubMed Scopus (241) Google Scholar), leading to the sulfenic acid derivative.A highly abundant plasma protein, it consumes a fraction of intravascular peroxynitrite but cannot outcompete the reaction with CO2.Oxyhemoglobin2.3 × 104It isomerizes peroxynitrite to nitrate (99Romero N. Radi R. Linares E. Augusto O. Detweiler C.D. Mason R.P. Denicola A. Reaction of human hemoglobin with peroxynitrite. Isomerization to nitrate and secondary formation of protein radicals.J. Biol. Chem. 2003; 278: 44049-44057Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar).It is relevant for peroxynitrite detoxification in red blood cells. At a concentration of 5 mm, k[oxy-Hb] = 340 s−1, a remarkable velocity. However, peroxiredoxin-2 outcompetes oxyhemoglobin in peroxynitrite detoxification in the erythrocyte (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar).Mn-SOD>104The reaction of peroxynitrite anion with the Mn2+ atom produces enzyme nitration at Tyr-34 (43Quijano C. Hernandez-Saavedra D. Castro L. McCord J.M. Freeman B.A. Radi R. Reaction of peroxynitrite with Mn-superoxide dismutase. Role of the metal center in decomposition kinetics and nitration.J. Biol. Chem. 2001; 276: 11631-11638Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar).The nitration of the critical Tyr residue leads to enzyme inactivation. This process is largely observed in vivo under inflammatory conditions.CO25.8 × 104Nucleophilic addition of peroxynitrite anion to CO2 yields an unstable intermediate that undergoes homolysis (35Lymar S.V. Hurst J.K. Rapid reaction between peroxynitrite ion and carbon dioxide: implications for biological activity.J. Am. Chem. Soc. 1995; 117: 8867-8868Crossref Scopus (494) Google Scholar, 36Denicola A. Freeman B.A. Trujillo M. Radi R. Peroxynitrite reaction with carbon dioxide/bicarbonate: kinetics and influence on peroxynitrite-mediated oxidations.Arch. Biochem. Biophys. 1996; 333: 49-58Crossref PubMed Scopus (505) Google Scholar, 38Bonini M.G. Radi R. Ferrer-Sueta G. Ferreira A.M. Augusto O. Direct EPR detection of the carbonate radical anion produced from peroxynitrite and carbon dioxide.J. Biol. Chem. 1999; 274: 10802-10806Abstract Full Text Full Text PDF PubMed Scopus (280) Google Scholar).This is a central reaction controlling peroxynitrite reactivity in biological system. A k[CO2] value of ∼60–100 s−1 has been established as a desirable starting range for a peroxynitrite scavenger to be competitive (13Ferrer-Sueta G. Radi R. Chemical biology of peroxynitrite: kinetics, diffusion, and radicals.ACS Chem. Biol. 2009; 4: 161-177Crossref PubMed Scopus (598) Google Scholar).AconitaseePeroxynitrite also causes aconitase tyrosine nitration, but this is not related to the loss of activity, which is exclusively due to the oxidation of the [4Fe-4S] cluster (59).1.4 × 105Oxidation and disruption of the iron-sulfur cluster (57Hausladen A. Fridovich I. Superoxide and peroxynitrite inactivate aconitases, but nitric oxide does not.J. Biol. Chem. 1994; 269: 29405-29408Abstract Full Text PDF PubMed Google Scholar, 58Castro L. Rodriguez M. Radi R. Aconitase is readily inactivated by peroxynitrite, but not by its precursor, nitric oxide.J. Biol. Chem. 1994; 269: 29409-29415Abstract Full Text PDF PubMed Google Scholar)A key reaction in mitochondria, aconitase inactivation slows down the Krebs cycle and causes iron release.Peroxiredoxins10
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