Superoxide anions do not react with hydroperoxides

Bors, Wolf; Michel, Christa; Sarán, Manfred

doi:10.1016/0014-5793(79)80417-2

Cited by 44 publications

(10 citation statements)

References 21 publications

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“…This reaction, too, has a positive Gibbs energy, but more importantly, in 1947 George (53), and later several other groups (54)(55)(56)(57)(58)(59) showed that, compared with the rate of superoxide dismutation (60), the reaction, even with triplet oxygen as a product, is too slow to be relevant.…”

Section: Discussionmentioning

confidence: 99%

Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )

Martinez

Mascio

Bonini

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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], peroxynitrite (ONOO ؊ ) decomposes after protonation to singlet oxygen ( 1 ⌬gO2) and singlet oxonitrate (nitroxyl, 1 NO ؊ ) in high yield. They claimed to have observed nitrosyl hemoglobin from the reaction of NO ؊ with methemoglobin; however, contamination with hydrogen peroxide gave rise to ferryl hemoglobin, the spectrum of which was mistakenly assigned to nitrosyl hemoglobin. We have carried out UV-visible and EPR experiments with methemoglobin and hydrogen peroxide-free peroxynitrite and find that no NO ؊ is formed. With this peroxynitrite preparation, no light emission from singlet oxygen at 1270 nm is observed, nor is singlet oxygen chemically trapped; however, singlet oxygen was trapped when hydrogen peroxide was also present, as previously described [Di Mascio, P., Bechara, E. )] is an inorganic oxidant of biological importance that is produced from superoxide and nitrogen monoxide (1). The mechanisms by which peroxynitrite or peroxynitrous acid [pK a ϭ 6.7 at 37°C (2)] oxidizes biomolecules are being investigated by various groups. There are two types or reaction: reactions between biomolecules and peroxynitrite (or peroxynitrous acid) that are first-order in peroxynitrite and in the biomolecule, and reactions that are first-order in peroxynitrite and zero-order in the biomolecule. In the latter case, either peroxynitrous acid undergoes homolysis to nitrogen dioxide and the hydroxyl radical (3-7), or it forms an activated intermediate (2,8). In the absence of oxidizable molecules the radicals recombine to nitrate, or the activated intermediate undergoes an internal isomerization. The rate constant for this process, which is first-order in peroxynitrite, is 3.9 s Ϫ1 at 37°C (2). Whether radicals are intermediates is not relevant for the present discussion. All involved agree that at acid pH and at low temperatures peroxynitrous acid isomerizes to nitrate quantitatively, whereas at higher pH nitrite and dioxygen in a 2 to 1 ratio also are found.Recently, a mechanism was proposed, in which peroxynitrite forms, after protonation, a cyclic intermediate, which dissociates to form oxonitrate(1Ϫ)-the commonly used name ''nitroxyl'' is outdated-and singlet oxygen (9):These products have been postulated before by Khan (10). As described in the more recent article (9), Khan et al. used methemoglobin (MetHb) to trap oxonitrate(1Ϫ), and 9,10-diphenylanthracene and 2,3-dimethyl-2-butene to trap singlet oxygen. Their mechanism does not explain the quantitative formation of nitrate, and we therefore investigated how these results (9) could have been obtained. We show here that singlet oxygen is not formed when peroxynitrite free of hydrogen peroxide is used, that the evidence for oxonitrate(1Ϫ) is based on a misinterpretation of the hemoglobin UV-visible spectra, and that the formation of these products and the postulated cyclic precursor, 4-hydrido-4-azy-1,2,3-trioxy[04]cycle, or trioxazetidine, is thermodynamically unlikely. The experimental evidence presented by Khan et al. (9) is best explained by the presence...

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Section: Discussionmentioning

confidence: 99%

Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )

Martinez

Mascio

Bonini

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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“…A Fenton-type reaction involving lipid hydroperoxide reduction would yield alkoxyl radicals (RO') [3]. With superoxide (7) or ferrous iron (8) as the reductant we have respectively:…”

Section: (A) Alkoxyl Radical Formationmentioning

confidence: 99%

“…O~ + ROOH ---~ RO" + OH-+ 02 (7) Fe ÷2 + ROOH ----+ RO' + OH-+ Fe ÷3 (8) Whether superoxide can directly reduce lipid peroxides (Eqn. 7) is controversial [8,44].…”

Section: (A) Alkoxyl Radical Formationmentioning

confidence: 99%

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Photooxidative reactions in chloroplast thylakoids. Evidence for a Fenton-type reaction promoted by superoxide or ascorbate

Upham

Jahnke

1986

Photosynth Res

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A methyl viologen (MV)(*) mediated Mehler reaction was studied using Type C and D chloroplasts (thylakoids) from spinach. The extent of photooxidative reactions were measured as (a) rate of ethylene formation from methional oxidation indicating the production of oxygen radicals, and (b) rate of malondialdehyde (MDA) formation as a measure of lipid peroxidation. Without added ascorbate, 1 μM FerricEDTA increased ethylene formation by greater than 4-fold, but had no effect on MDA production. Ascorbate (1 mM) produced a tripling of ethylene while it reduced MDA formation in the presence of iron. Radical scavengers diethyldithiocarbamate (DDTC), formate, 1,4-diazabicyclo (2.2.2octane) (DABCO), inhibited ethylene formation. Using 0,4 M mannitol to scavenge hydroxyl radicals, the rates of ethylene formation were reduced 40 to 60% with or without 1 μM Fe(III) EDTA. The strong oxidant(s) not scavenged by mannitol are hypothesized to be either alkoxyl radicals from lipid peroxidation, or 'site specific' formation of hydroxyl radicals in a lipophillic environment not exposed to mannitol. Singlet oxygen does not appear to be a significant factor in this system. Catalase strongly inhibited both ethylene and MDA synthesis under all conditions; 1 mM ascorbate did not reverse this inhibition. However, the strong superoxide dismutase (SOD) inhibition of ethylene and MDA formation was completely reversed by 1 mM ascorbate. This suggests that superoxide was functioning as an iron reducing agent and that in its absence, ascorbate was similarly promoting oxidations. Therefore, these oxidative processes were dependent on the presence of H2O2 and a reducing agent, suggesting the involvement of a Fenton-type reaction.

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“…George showed already in 1947 that the second reaction is too slow in comparison to the disproportionation of superoxide 4 . Nevertheless, a number of groups, unaware of George's work (see also [5][6][7] , set out in the early seventies to determine the rate constant of Reaction 2, and all concluded, like George, that the rate constant was of the order of 1 M , or smaller [8][9][10][11][12][13][14] . The recent suggestion 15 that Reaction 2 is significant and that the dioxygen is produced in the 1 ∆ g singlet state must be rejected as erroneous on kinetic and thermodynamic grounds.…”

Section: The Chemistry Of Peroxynitrite a Biological Toxin Introductionmentioning

confidence: 99%

The chemistry of peroxynitrite, a biological toxin<a name=TOP1></a>

Koppenol¹

1998

Quím. Nova

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Recebido em 22/8/97Oxyradicals play a role in several diseases. While for several decades the hydroxyl radical -produced via the Fenton reaction -has been considered the species that initiates oxyradical damage, new findings suggest that much of this damage can be ascribed to peroxynitrite, O=NOO -, formed from the reaction of the superoxide anion with nitrogen monoxide near activated macrophages. The rate constant for the reaction of this reaction has been investigated by flash photolysis and was found to be significantly higher than previously described in the literature, 1.9 x 10 10 M -1 s -1 . Studies of the isomerization to nitrate resulted in the discovery of a complex between peroxynitrite and its protonated form with a stability constant of 1 x 10 4 M -1 . Some of the harmful reaction of peroxynitrous acid have been ascribed to the hydroxyl radical as a product of homolysis of the O-O bond during the conversion to nitrate. Kinetics of the isomerization reaction as a function of pressure show that the activation volume is only +1.5+1.0 ml mol -1 , which is inconsistent with homolysis. Instead, an intermediate, possibly a distorted trans-isomer of O=NOOH could be responsible for the harmful reactions of peroxynitrite.

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Superoxide anions do not react with hydroperoxides

Cited by 44 publications

References 21 publications

Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )

Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )

Photooxidative reactions in chloroplast thylakoids. Evidence for a Fenton-type reaction promoted by superoxide or ascorbate

The chemistry of peroxynitrite, a biological toxin<a name=TOP1></a>

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Superoxide anions do not react with hydroperoxides

Cited by 44 publications

References 21 publications

Peroxynitrite does not decompose to singlet oxygen ( 1 Δ g O 2 ) and nitroxyl (NO − )

Peroxynitrite does not decompose to singlet oxygen ( 1 Δ g O 2 ) and nitroxyl (NO − )

Photooxidative reactions in chloroplast thylakoids. Evidence for a Fenton-type reaction promoted by superoxide or ascorbate

The chemistry of peroxynitrite, a biological toxin<a name=TOP1></a>

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Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )

Peroxynitrite does not decompose to singlet oxygen ( ¹ Δ _g O ₂ ) and nitroxyl (NO ⁻ )