Interactions of Thiyl Free Radicals with Oxygen: A Pulse Radiolysis Study

Tamba, Maurizio; Simone, Giuseppina De; Quintiliani, M.

doi:10.1080/09553008614550991

Cited by 95 publications

(38 citation statements)

References 4 publications

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“…4) provide evidence that a major overall pathway following direct excitation of GSNO is formation of GSSG. This is in agreement with previous studies of both GSNO decomposition (14) and pulse radiolysis of GSH (28). However, transient absorption spectroscopy has provided clear evidence that the mechanism does not simply involve homolysis and subsequent GS recombination.…”

Section: Hbo2supporting

confidence: 92%

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The Mechanism of Photochemical Release of Nitric Oxide from S‐Nitrosoglutathione

Wood

Mutus

Redmond

1996

Photochem & Photobiology

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Abstract— Laser flash photolysis of S‐nitroso complexes of glutathione (GSNO) and bovine serum albumin (BSANO) via excitation at 355 nm has been used to investigate the photogeneration of nitric oxide (NO) and subsequent radical reactions. In the case of GSNO, liberation of NO was confirmed by its oxidation of oxyhemoglobin to met hemoglobin. Initial NO release is via homolytic cleavage of the S‐N bond to produce the glutathione thiyl radical, GS, which can subsequently react with (a) ground‐state GSNO (k= 1.7 × 109M−1/i> s−1) to yield additional NO and oxidized glutathione, GSSG; and (b) oxygen (k= 3.0 × 109M−1 s−1) to give the glutathione peroxy radical, GSOO, which subsequently reacts with ground‐state GSNO (k= 3.8 × 108M−1 s−1), also producing additional NO and GSSG. The relative concentrations of oxygen and GSNO in the system determine the major pathway for removal of G'. These secondary reactions occur at such high rates that they preclude radical recombination under low‐intensity irradiation conditions. The quantum yield of overall loss of GSNO thus varies with both GSNO and oxygen concentrations; a value of 0.66 was determined for an aerated solution of GSNO (0.86 mM). In the case of GSNO, therefore, generation of NO is not due solely to homolysis of the S‐N bond; secondary reactions of the radicals formed lead to further NO liberation. In rationalizing the known phototoxicity of GSNO, possible contributions from thiyl and thiyl‐derived radicals should be considered. In contrast to GSNO, direct excitation of BSANO (containing one bound NO group per molecule) led to photodecomposition with a quantum yield of 0.09 but no evidence was obtained for liberation of NO into the bulk medium.

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Section: Hbo2supporting

confidence: 92%

“…In aerated or oxygen-saturated solutions the species GSOO, formed via reaction between G S and oxygen (Eq. 3) was detected by its characteristic absorption, peaking at 540 nm (28) (Fig. 3).…”

Section: Effect Of Oxygenmentioning

confidence: 99%

The Mechanism of Photochemical Release of Nitric Oxide from S‐Nitrosoglutathione

Wood

Mutus

Redmond

1996

Photochem & Photobiology

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“…Although the sink hypothesis is kinetically and thermodynamically feasible [66], the sulfur centered radical can also react rapidly with oxygen producing species that could be competent for other, possibly damaging, reactions [67]. …”

Section: Can Free Radicals Be Efficiently Scavenged Under Biologicmentioning

confidence: 99%

How do nutritional antioxidants really work: Nucleophilic tone and para-hormesis versus free radical scavenging in vivo

Forman

Davies

Ursini

2014

Free Radical Biology and Medicine

604

523

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We present arguments for an evolution in our understanding of how antioxidants in fruits and vegetables exert their health-protective effects. There is much epidemiological evidence for disease prevention by dietary antioxidants and chemical evidence that such compounds react in one-electron reactions with free radicals in vitro. Nonetheless, kinetic constraints indicate that in vivo scavenging of radicals is ineffective in antioxidant defense. Instead, enzymatic removal of non-radical electrophiles, such as hydroperoxides, in two-electron redox reactions is the major antioxidant mechanism. Furthermore, we propose that a major mechanism of action for nutritional antioxidants is the paradoxical oxidative activation of the Nrf2 (NF-E2-related factor 2) signaling pathway, which maintains protective oxidoreductases and their nucleophilic substrates. This maintenance of ‘Nucleophilic Tone,’ by a mechanism that can be called ‘Para-Hormesis,’ provides a means for regulating physiological non-toxic concentrations of the non-radical oxidant electrophiles that boost antioxidant enzymes, and damage removal and repair systems (for proteins, lipids, and DNA), at the optimal levels consistent with good health.

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“…However, RSOO' is not considered to be a good hydrogen abstractor (Sevilla et al 1990b) although one report suggests that it is an effective one-electron oxidant (Tamba et al 1986) . ESR work has shown that RSOO' is involved in a cyclic reaction sequence (reaction 6) which results in a highly reactive intermediate RS0 200' (Sevilla et al 1988(Sevilla et al , 1990a(Sevilla et al , 1990b .…”

Section: Rs' +Rsh Rssr' -+ H +mentioning

confidence: 98%

“…An alternative hypothesis is that the radical reactions of thiols in the presence of oxygen are the source of the COEE . In one model formation of thiol peroxyl radicals (RSOO') (Quintiliani 1983, 1986, Priitz and Monig 1987 in an equilibrium (reaction 5) (Tamba et al . 1986, Wardman 1988, has two consequences : (1) RSSR' -formation is suppressed as is any repair it may accomplish, and (2) RSOO' may itself lead to DNA inactivation (Priitz and .…”

Section: Rs' +Rsh Rssr' -+ H +mentioning

confidence: 98%

Influence of Oxygen on the Repair of Direct Radiation Damage to DNA by Thiols in Model Systems

Becker

Summerfield

Gillich

et al. 1994

International Journal of Radiation Biology

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Here the reactions of thiols with DNA primary radical intermediates formed after gamma-irradiation of frozen (77 K) anoxic and oxic solutions of DNA/thiol mixtures are investigated. Through analysis of the experimental composite spectra at each annealing temperature, the relative concentrations of individual radicals present are estimated and reaction sequences inferred. In all samples the primary DNA radical anions and cations (DNA.+ and DNA.-) are suggested to be the predominant radicals at low temperatures. In anoxic samples, TH. (5,6-dihydrothym-5-yl radical), .RSSR.- and, in glutathione samples, .GSH [gamma-glu-NHC(CH2SH)CO-gly] radicals are observed as the temperature is increased. The presence of oxygen efficiently suppresses the formation of RSSR.- and .GSH; instead, in oxic samples, O2.-, DNAOO., RSOO. and RSO. are observed at higher temperatures. The photolytic conversion of RSOO. to RSO2. is used to verify the presence of RSOO. in gamma-irradiated DNA/thiol systems and confirm that the computer analysis employed yields reasonable estimates of the relative DNAOO. and RSOO. concentrations. From the relative concentrations of radicals present, it is clear that the radicals observed at higher temperatures originate from the radical reactions of the primary DNA.+ and DNA.- radicals. Based on the reaction sequences inferred and previous work with thiols alone, it is concluded that TH., DNAOO. and RSOO. (in part) originate largely with DNA.-, whereas RSSR.-, .GSH and RSOO. (in part) originate largely with DNA.+. The possible roles of DNAOO., RSOO., RSO., RSO2. and .OOGSH in the chemical oxygen enhancement effect at biologically realistic temperatures are discussed.

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Interactions of Thiyl Free Radicals with Oxygen: A Pulse Radiolysis Study

Cited by 95 publications

References 4 publications

The Mechanism of Photochemical Release of Nitric Oxide from S‐Nitrosoglutathione

The Mechanism of Photochemical Release of Nitric Oxide from S‐Nitrosoglutathione

How do nutritional antioxidants really work: Nucleophilic tone and para-hormesis versus free radical scavenging in vivo

Influence of Oxygen on the Repair of Direct Radiation Damage to DNA by Thiols in Model Systems

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