Mechanism of the disproportionation of ascorbate radicals

Bielski, Benon H. J.; Allen, Augustine O.; Schwarz, Harold A.

doi:10.1021/ja00402a042

Cited by 198 publications

(149 citation statements)

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“…It was found that this reaction significantly affects the reduction of TEMPO-derivatives of the NR of piperidine type [27] in alkaline medium. However, in most cases the main source of the formation of dehydroascorbic acid is the reaction (3) of the ascorbate radical dismutation studied in details by Bielski et al [35]. The following dehydroascorbic acid decomposition to diketogulonic acid, described by the reaction (4), was discussed in the literature [37,38].…”

Section: Discussionmentioning

confidence: 99%

“…(1)- (5) to the experimental data were obtained (see Figures 2, 3, 6 and 7). The rate constant k 3 for the reaction of ascorbate radical dismutation was calculated using literature data [35] for the experimental values of pH and ionic strength of solution. In its turn, the equilibrium constant K 3 for the reaction (3) was found to be equal to (4.2±0.8) × 10 −9 M −1 s −1 being within the range (10 −9 − 10 −8 ) M −1 s −1 reported in the literature [39].…”

Section: Discussionmentioning

confidence: 99%

“…Under these conditions steady-state concentration of the ascorbate radical was observed for at least 10 min. The EPR spectra were recorded with the following spectrometer settings: scan time 41 , where k 3 is bimolecular rate constant of the dismutation reaction [35]. It was found that the rate V is proportional to the enzyme concentration in the experimental concentration range.…”

Section: The Ascorbate Radical Generating Systemmentioning

confidence: 99%

“…This simple equation was used to calculate the observed rate constant, k obs = k GSH ·[GSH], from the steady-state concentrations of ascorbate radical measured in the absence and in the presence of GSH. The rate constant, k 3 , of ascorbate radical dismutation was calculated from Bielski et al [35] for the values of pH and ionic strength of the solution used in the sample preparation.…”

Section: The Ascorbate Radical Reaction With Glutathionementioning

confidence: 99%

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Reversible reduction of nitroxides to hydroxylamines: Roles for ascorbate and glutathione

Bobko

Kirilyuk

Grigor'ev

et al. 2007

Free Radical Biology and Medicine

134

123

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Biological applications of stable nitroxyl radicals, NR, include their use as contrast agents for magnetic resonance imaging, spin labels, superoxide dismutase mimics, and antioxidants. The rapid reduction of NR in biological samples into hydroxylamines, HA, significantly limits their application. In its turn, reoxidation of HA back to the NR has been used for detection of reactive oxygen species, ROS. In this work comparative studies of the reduction of pyrrolidine, imidazoline and imidazolidine NR by ascorbate were performed taking advantage of recently synthesized tetraethyl substituted NR with much higher stability towards reduction both in vitro and in vivo. Surprisingly, these NR kept 10-50% of initial intensity of electron paramagnetic resonance signal for about 1 h in the presence of hundred fold excess of ascorbate. To explain this data, reoxidation of the corresponding HA by ascorbate radical and dehydroascorbic acid back to the NR was proposed. This hypothesis was supported by direct measurement of the NR appearance from the HA upon ascorbate radical generation by ascorbate oxidase, or in the presence of the dehydroascorbic acid. The reversible reaction between NR and ascorbate was observed for the various types of the NR, and the rate constants for direct and reverse reactions were determined. The equilibrium constants for oneelectron reduction of the tetraethyl substituted NR by ascorbate were found to be in the range from 2.65×10 −6 to 10 −5 which is significantly lower than corresponding values for the tetramethyl substituted NR (less or about 10 −4 ). This explains an establishment of EPR-detectable quasiequilibrium level of tetraethyl substituted NR in the presence of excess of ascorbate. The redox reactions of the NR-HA couple in ascorbate containing medium was found to be significantly affected by glutathione, GSH. This effect was attributed to the reduction of ascorbate radical by GSH, and the rate constant of this reaction was found to be equal to 10 M −1 s −1 . In summary, the data provide new insight into the redox chemistry of NR and HA, and significantly affect interpretation and strategy of their use as redox-and ROS-sensitive probes, or as antioxidants.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: The Ascorbate Radical Generating Systemmentioning

confidence: 99%

Section: The Ascorbate Radical Reaction With Glutathionementioning

confidence: 99%

See 2 more Smart Citations

Reversible reduction of nitroxides to hydroxylamines: Roles for ascorbate and glutathione

Bobko

Kirilyuk

Grigor'ev

et al. 2007

Free Radical Biology and Medicine

134

123

View full text Add to dashboard Cite

show abstract

“…Whether or not superoxide is itself toxic is debatable on present evidence [ 15]. However, it cannot be considered innocuous since it appears to produce hydroxyl radicals from hydrogen peroxide in the presence of catalytic iron complexes [16].…”

Section: Methodsmentioning

confidence: 95%