The effect of pH and complexation on redox reactions between RS• radicals and flavins

Ahmad, Rizwan

doi:10.1139/v84-035

Cited by 29 publications

(9 citation statements)

References 16 publications

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“…Given that theoretical considerations have indicated that the thiyl radical redox couple RS-/RS-has a one-electron potential of approx. 1.0 V, this provides further support for an electron-transfer mechanism (Ahmad & Armstrong, 1984).…”

Section: Gs + Nadh --Gs-+ Nadh + (25)supporting

confidence: 63%

Thiyl and phenoxyl free radicals and NADH Direct observation of one-electron oxidation

Forni¹,

Willson²

1986

Biochemical Journal

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Absolute rate constants for the reaction of NADH with thiyl free radicals derived from various sulphurcontaining compounds of biological significance were measured by using the technique of pulse radiolysis. These and related reactions with phenoxyl free radicals are believed to occur through one-electron-transfer processes. Further evidence comes from studies with deuterated NADH. The results support the possibility that, in biochemical systems, thiols may act as catalysts linking hydrogen-atom and electron-transfer reactions.

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Section: Gs + Nadh --Gs-+ Nadh + (25)supporting

confidence: 63%

Thiyl and phenoxyl free radicals and NADH Direct observation of one-electron oxidation

Forni¹,

Willson²

1986

Biochemical Journal

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“…However, we observed no evidence for Of formation in the quenching of 10 2 by the cellular reducing agents, cysteine and glutathione. On thermodynamic grounds this is again reasonable because Ahmad and Armstrong [49] have estimated that E ° (RS'/RS-~)= +1.1 V, while for ~O 2 the one-electron reduction potential has been estimated to be E ° (102/Of) = +0.65 V [48]. Thus, the one-electron reduction of 10 2 by cysteine is highly unlikely.…”

mentioning

confidence: 77%

Superoxide, hydrogen peroxide and singlet oxygen in hematoporphyrin derivative-cysteine, -NADH and -light systems

Buettner

Hall

1987

Biochimica et Biophysica Acta (BBA) - General Subjects

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Hematoporphyrin derivative and light in the presence of cysteine or glutathione were found to convert oxygen to superoxide and hydrogen peroxide at pH < approx. 6.5, while at pH > 6.5 no superoxide or hydrogen peroxide production was observed. However, at pH values greater than 6.5 the rate of oxygen consumption increased. This rate paralleled the acid dissociation curve of the cysteine thioi group and is consistent with the chemical quenching of tO z by cysteine. The superoxide and hydrogen peroxide formation observed below pH 6.5 appeared not to be related to the singlet oxygen production of hematoporphyrin derivative. In addition, superoxide and hydrogen peroxide production was observed with hematoporphyrin derivative and light in the presence of NADH, both above and below pH 6.5. Direct detection of singlet oxygen luminescence at 1268 nm in the hematoporphyrin derivative-light system (2HzO as solvent) revealed an apparent linear increase in the singlet oxygen emission intensity as the pZH was raised from 7.0 to 10.0. Azide efficiently quenched this observed emission. In addition, at p2H 7.4, 1 mM cysteine resulted in a 40% reduction of the singlet oxygen luminescence, while at pZH 9.4 the signal was quenched by over 95% (under the experimental conditions employed). In total, we interpret these results as consistent with the chemical quenching of to z by the ionized thiol group of cysteine.

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“…However, it is evident that this species would have to be an intermediate in the twoelectron reduction of F1 by RSSR-in the presence of RSH at pH 9 or 10, and the only significant product of that reaction was FlH- (14). Therefore it is evident that RSHF1.-is a fairly labile species, possible reacting with RS -as follows.…”

Section: Fad At P Hmentioning

confidence: 97%

Formation and spectra of flavin radicals in the presence of β-mercaptoethanol at pH 9 and 10

Surdhar¹,

Ahmad²

1984

Can. J. Chem.

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Can. J. Chem. 62, 580 (1984). Spectral changes and rates of reaction of flavins and several radical species have been investigated at pH 7, 9, and 10 in the presence and absence of P-mercaptoethanol. The radicals .C02-, e,,-, and LS;-reacted with FAD at pH 10 to give a spectrum of FAD .FI-with rate constants of 7 ? 1 x 10' and 4 ? 1 x IOX M ' s ' for . C O i and LS;-respectively. At pH 7 only .FIH was observed and at pH 9 a mixture of .FIH and .FI-.Interactions between flavin radicals and sulphydryl at M concentration did not cause perturbations in the uv-visible spectra until either the radical and/or the sulphydryl were ionized. With FAD at pH 9 or 10 and LFI at pH 10 the 370 nm peak of .FI-was enhanced by about 15% and a second larger growth occurred near 450 nm in the presence of to M sulphydryl. We attribute this to the formation of labile intermediate RSHFl .-, which must also be involved in the reduction of F1 by RSSR-at pH 9 or 10. The second order rate constant k13 for reaction of RSSR-with FAD at pH 9 and 10 was found to be 4.2 2 0.5 x lo%-' s-' and 2.0 +-0.4 X 10' M -' s-' respectively. The rate constant for the reaction between RSSR-and LFI at pH 10 was slightly faster, 7 * 1 X

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The effect of pH and complexation on redox reactions between RS• radicals and flavins

Abstract: . On considkre brikvement les effets des changements observes dans les propriCtCs redox des radicaux sulfurts sur la complexation avec RS-et sur la protonation.[Traduit par le journal]

Cited by 29 publications

References 16 publications

Thiyl and phenoxyl free radicals and NADH Direct observation of one-electron oxidation

Thiyl and phenoxyl free radicals and NADH Direct observation of one-electron oxidation

Superoxide, hydrogen peroxide and singlet oxygen in hematoporphyrin derivative-cysteine, -NADH and -light systems

Formation and spectra of flavin radicals in the presence of β-mercaptoethanol at pH 9 and 10

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