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M Saran

Publications and source records attributed to M Saran.

At least 19 recordsLinked to original sources
PubMed1991

Direct and indirect measurements of oxygen radicals.

Instead of covering the available detection methods in detail it is attempted to highlight the ambiguities inherent in oxygen radical detection under in vivo conditions. Due to physicochemical properties of the oxygen molecule, all organic matter is bound to autoxidize. From this it follows that a certain 'background' level of oxygen radical production will always be present and that it may be difficult to differentiate between inherent and induced oxygen radical production. Radicals by their very nature react 'unspecifically'. This infers that it is difficult to identify them unequivocally. The most common methods for oxygen radical detection are briefly mentioned.

Animals↗
PubMed1991

An expanded function for superoxide dismutase.

alpha-Hydroxyalkylperoxyl radicals were generated from the primary and secondary alcohols methanol, ethanol and 2-propanol in N2O/O2-saturated aqueous solutions by pulse radiolysis. These radicals reduced a ferric iron porphyrin complex, tetrakis-(4-N-methylpyridyl)porphine, with diffusion-controlled rate constants. The extreme sensitivity of the shift of the Soret absorption band in this reaction was used to determine, by competition kinetics, the reactivity of the peroxyl radicals with different proteins. Only native Cu,Zn-superoxide dismutase and metallothionein showed competitive behavior, with SOD exhibiting rate constants close to the dismutation rate for O2-. Metallothionein was slower by a factor of 30 with hydroxymethylperoxyl radicals. We propose, that SOD has unique properties of the protein surface in addition to the prosthetic copper site, having possibly evolved as a 'general-purpose radical-scavenging protein'.

Alcohols↗
PubMed1990

Radical reactions in vivo--an overview.

Generation of radicals in vivo depends on metabolic activities. The reactions are usually influenced by (i) the presence and concentration of oxygen; (ii) the availability of transition metals (effects of binding and compartimentalization); (iii) the level of reductants and antioxidants (e.g. nutritional effects). The effects of radicals are thought to be due to (i) membrane damage (affecting passive or active transport through altered fluidity/function interrelationships, intercellular messenging through modifications in the synthesis of prostaglandins and leukotrienes); (ii) protein damage (e.g. affecting membrane transporters, channel proteins, receptor or regulatory proteins, immunomodulators); (iii) damage to DNA. Defense mechanisms consist of (i) prevention of the 'spreading' of primary damage by low molecular weight antioxidants (e.g. vitamin E, GSH, vitamin C, beta-carotene, uric acid); (ii) prevention or limitation of 'secondary' damage by enzymes (e.g. GSH-peroxidase, catalase, superoxide dismutase, DT-diaphorase) and/or chelators; (iii) repair processes, e.g. lipid degradation/membrane repair enzymes (phospholipases, peroxidases, some transferases and reductases), protein disposal or repair enzymes (proteases, GSSG-reductase), DNA degradation repair enzymes (exonuclease III, endonucleases III and IV, glycosylases, polymerases). Recent hypotheses on a messenging function of the superoxide anion O2- are discussed and possible implications of cross-reactions between O2- and nitric oxide (endothelium-derived relaxing factor EDRF) are shortly mentioned.

Antioxidants↗
PubMed1990

Calcium in lipid peroxidation: does calcium interact with superoxide?

Using a pulse radiolysis approach to generate and observe superoxide anions (O2-.) in the absence and presence of calcium, we have attempted to verify the recent hypothesis of Babizhayev (Arch. Biochem. Biophys. 266, 446-451, 1988) of a Ca2(+)-O2-. interaction during lipid peroxidation. We could not observe rapid scavenging of O2-. or complex formation with Ca2+ to account for an inhibitory effect of this cation on lipid peroxidation. Neither could we agree that the stimulatory effect is due to liberation of catalytic ferrous iron from weak complexes by Ca2+. Drawing on reports in the literature, we propose an alternate explanation for the apparent stimulation of lipid peroxidation by low Ca2+ concentrations. In our view, this is not a direct effect, but reflects independently initiated processes of lipid peroxidation and Ca2+ translocation, which interact subsequently in a synergistic manner. The reported inhibition at high Ca2+ concentrations is considered an artifact as it was observed at levels far in excess of those relevant to animal systems (but not necessarily in some plant compartments).

Acetates↗
PubMed1990

Reaction of NO with O2-. implications for the action of endothelium-derived relaxing factor (EDRF).

Under physiological pH conditions (pH 7.2-7.4) the rate constant of the reaction NO + O2- yielding peroxonitrite (ONOO-) was determined as k = (3.7 +/- 1.1) x 10(7) M-1 s-1. The decay of peroxonitrite at this pH follows first order kinetics with a rate constant of 1.4 s 1. At alkaline pH peroxonitrite is practically stable. Possible consequences of these reactions for the biological lifetime of EDRF will be discussed.

Hydrogen-Ion Concentration↗
PubMed1989

The mechanism of cytochrome C reduction by alkyl radicals. Evidence for multiple reaction pathways.

The reactions of the hydroxyalkyl radicals .CH2OH and (CH3)2.COH with oxidized cytochrome c are for more complex than previously reported. Analysis of the pulse-radiolytic data by kinetic modelling revealed that only about 40% of the alkyl radicals reduce the ferric iron chromophore. Altogether, four different reactions have to be considered for the disappearance of the alkyl radicals, only two of which affect the metal site. The data show that these radicals, similar to the much more reactive hydrated electrons and hydrogen atoms, are capable to react with biological macromolecules in diverse ways.

Cytochrome c Group↗
PubMed1989

Oxygen radicals acting as chemical messengers: a hypothesis.

Based on a critical reappraisal of the reactions of radicals in a biological milieu, a hypothesis is proposed according to which superoxide anion radicals act as biological messengers rather than as mediators or precursors of cellular damage under oxidative stress conditions.

Animals↗
PubMed1988

A critical reevaluation of some assay methods for superoxide dismutase activity.

We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide dismutase activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O2- are generated, the "turnover" rate constant, kcat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O2- are formed, the value of kcat determined by these methods, can be orders of magnitude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.

Copper↗
PubMed1987

Determination of sulfite radical (SO.3-) reaction rate constants by means of competition kinetics.

The sulfite radical anion (SO.3-) was found to react rapidly with the flavonoid quercetin (k = 2.5 x 10(8) dm3mol-1s-1) and the carotenoids crocin (k = 1.0 x 10(9) dm3mol-1s-1) and crocetin (k = 1.5 x 10(9) dm3mol-1s-1). The reactions can easily be monitored due to the strong absorptions of the substrates and, in the case of quercetin, the formation of a strongly absorbing transient species. Using these substances, we determined by means of competition kinetics rate constants of SO.3- reactions with nucleic acid components, polyunsaturated fatty acids, and glutathione.

Carotenoids↗
PubMed1987

Reactions of linoleic acid peroxyl radicals with phenolic antioxidants: a pulse radiolysis study.

Linoleic acid peroxyl radicals (LOO.) can be viewed as model intermediates occurring during lipid peroxidation processes. Formation and reactions of these species were investigated in aqueous alkaline solution using the technique of pulse radiolysis combined with kinetic spectroscopy. Irradiation of linoleic acid in N2O/O2-saturated solutions leads to a mixture of peroxyl radical isomers, whereas reaction of 13-hydroperoxylinoleic acid (13-LOOH) with azide radicals in N2O-saturated solution produces 13-LOO. radicals specifically. These peroxyl radicals cannot be observed directly, but their reactions with the two flavonols, kaempferol and quercetin, acting as radical-scavenging antioxidants, produced strongly absorbing aroxyl radicals (ArO.). The same aroxyl radicals were generated by .OH and N3. with rate constants exceeding 10(9) dm3 mol-1 s-1. Applying a reaction scheme that includes competing generation and decay reactions of both LOO. and ArO. radicals, we derived individual rate constants for LOO. reactions with the phenols (greater than 10(7) dm3 mol-1 s-1), with the aroxyl radicals to form covalent adducts (greater than 10(8) dm3 mol-1 s-1), as well as for their bimilecular decay (3.0 X 10(8) dm3 mol-1 s-1). These results demonstrate the high reactivity of both fatty acid peroxyl radicals and the flavone antioxidants in aqueous solution.

Antioxidants↗
PubMed1987

The reaction of sulfite radical anion with nucleic acid components.

The sulfite radical anion (SO3.-) is the first intermediate in the autoxidation of sulfite to sulfate. Using competition kinetics, its reactivities with the nucleic acid bases and the corresponding nucleosides were investigated. The second order rate constants were found to be rather low, k less than or equal to 1 x 10(6) dm3mol-1s-1 at pH 7. As a competitor, the carotenoid crocin was used, which was found to be bleached very efficiently by SO3.- (k = 1.0 x 10(9) dm3mol-1 s-1).

Carotenoids↗
PubMed1987

Radical scavenging by flavonoid antioxidants.

Aroxyl radicals of fifteen structurally distinct flavonoids were generated by attack of azide radicals (N3.) on the parent compounds dissolved in aqueous solution at pH 11.5. Generation rate constants were all found to be very high (2.4-8.8 x 10(9) dm3mol-1 s-1), whereas the decay rates differed considerably, ranging from 10(5) to 10(8) dm3mol-1 s-1. In most cases the spectral characteristics of the transient aroxyl radicals relate to structural features of the parent compounds and according to spectral similarities they can be classed in three distinct groups (with only two exceptions). Although the data do not conclusively prove that the biological function of flavonoids might be the scavenging of radicals, the very high rate constants of formation and the relative stability of some of the aroxyl radicals, are in support of such a hypothesis.

Antioxidants↗
PubMed1987

The kinetics of the reaction of ferritin with superoxide.

Using pulse radiolysis and competition kinetics with cytochrome c, the reaction of superoxide with horse spleen ferritin was investigated. The second-order rate constant is estimated to be 2 +/- 1 x 10(6) dm3 mol-1 s-1.

Cytochrome c Group↗
PubMed1979

Pulse-radiolytic investigations of catechols and catecholamines. II. Reactions of Tiron with oxygen radical species.

Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (.OH), superoxide anions (O-2) or a combination of both oxygen radicals. The rate constant with .OH radicals was determined at 1.0.10(9) M-1.s-1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11--16), the rate constant with O-2 of 1.0.10(7) M-1.s-1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with .OH and O-2 of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of .OH radicals, leading to the same products with catechol compounds.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed1979

On the nature of biochemically generated hydroxyl radicals. Studies using the bleaching of p-nitrosodimethylaniline as a direct assay method.

An efficient scavenger for radiolytically generated hydroxyl (OH) radicals, p-nitrosodimethylaniline, was used to try to substantiate the presence of this oxygen radical species in several biochemical systems. Most of these systems which were investigated had previously been assumed to generate OH radicals, e.g. the autoxidation of 6-hydroxydopamine, the hydroxylating system NADH/phenazine methosulfate, and the oxidation of xanthine or acetaldehyde by xanthine oxidase. We did not observe inhibition of the bleaching of p-nitrosodimethylaniline in oxygenated solutions by other scavengers of OH radicals nor, in the case of xanthine/xanthine oxidase, by catalase and superoxide dismutase. We therefore conclude that, under biochemical conditions as opposed to radiolysis or photolysis, no freely diffusable OH radicals are formed. Rather, a strongly oxidizing OH-analogous complex is considered to represent the p-nitrosodimethylaniline-detectable species formed under these conditions.

Acetaldehyde↗