The Reaction of Superoxide Radicals withS-Nitrosoglutathione and the Products of Its Reductive Heterolysis

Abstract

Generation of superoxide radicals (0.01-0.1 M s ؊1 ) by radiolysis of aqueous solutions containing S-nitrosoglutathione (45-160 M, pH 3.8 -7.3) resulted in loss of this solute at rates varying with solute concentration, radical generation rate, and pH. The results were quantitatively consistent with the loss being attributed to competition between reaction of superoxide with S-nitrosoglutathione (rate constant 300 ؎ 100 M ؊1 s ؊1 ) and the pH-dependent disproportionation of superoxide/hydroperoxyl. This rate constant is much lower than previous estimates and seven orders of magnitude lower than the rate constants between superoxide and superoxide dismutase or superoxide and nitric oxide. This indicates that interaction between superoxide and Snitrosoglutathione is unlikely to be biologically important, contrary to previous suggestions that reaction could serve to prevent the rapid reaction between superoxide and nitric oxide. Reductive homolysis of Snitrosoglutathione by the carbon dioxide radical anion, a model for biological reductants such as disulfide radical anions, occurred with a rate constant of 7.4 ؋ 10 8 M ؊1 s ؊1 and produced nitric oxide stoichiometrically. Thiyl radicals were not produced, indicating the alternative homolysis route to generate nitroxyl did not occur.

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

“…Transfer of NO from extracellular S-nitrosothiols to the cytosol may involve basically similar chemistry (Ramachandran et al, 2001), with N 2 O 3 as a nitrosating agent at the membrane/cytosol interface. S-nitrosothiols have low reactivity toward O 2 À (Ford et al, 2002b), but can release NO in tens of seconds in the presence of micromolar levels of Cu(II) under conditions where oxidized GSH (GSSG) does not stabilize the redox metal (Noble and Williams, 2000). It is important to note that there is less than one free copper ion per cell (Rae et al, 1999).…”

Reaction of hydroxyl radicals with S-nitrosothiols: Formation of thiyl radical (RS•) as the intermediate

“…(8)(9)(10) where the thiyl radical is the precursor of the respective disulfide. The dose-dependent decrease in the pH is a clear indication of the formation of HNO 2 .…”

“…•-), hydroxyl radicals ( • OH) and hydrate electron (e aq -) have been reported [8][9][10][11]. O 2 •-reacts with GSNO generating glutathionedisulphide (GSSG) and equimolar quantities of nitrite and nitrate [15].…”

“…In this context, the kinetics and mechanism of the release of • NO by RSNO is very important. The decomposition of RSNO by metal ions, light, some nucleophiles, and free radicals [3][4][5][6][7][8][9][10][11][12][13][14], is under extensive investigation in recent years. Among the decomposition reactions induced by free radicals, the reactions of superoxide radicals (O 2…”

Nitric oxide: To be or not to be an endocrine hormone?

“…Circulating SNOs can be decomposed in the presence of light, reducing agents including metal ion (eg Cu + ), ascorbate, superoxide anion (O 2 •− ) and thiols (eg glutathione) to release NO or contribute to transnitrosation reaction, in which NO transport between thiols to facilitate NO release; Cu 2+ ‐containing cell‐surface proteins (eg ceruloplasmin), protein disulphide isomerase, γ‐glutamyltransferase and S‐nitrosoglutathione (GSNO) reductase are also involved in NO release from SNOs . S‐nitrosoalbumin (SNO‐albumin) can release NO spontaneously (~1.4 pmol NO min −1 ) and this may be further potentiated in a temperature, light, ascorbate and thiol‐dependent manner .…”