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Query: HUMANGGP:001372 (ESR)
 7,313 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To understand the role of the superoxide (O-2) radical in chromate-related genotoxicity, we investigated whether Cr(VI) can catalyze the Haber-Weiss cycle in vitro: O-2 + Cr(VI)----Cr(V) + O2 Cr(V) + H2O2----Cr(VI) + .OH + OH-. ESR and spin trapping techniques were utilized to monitor the O-2 (produced using xanthine/xanthine oxidase), .OH, and Cr(V) species. Superoxide dismutase as well as catalase inhibited the .OH radical radical formation, attesting to the direct involvement of O-2 and H2O2 in the process. ESR measurements also provided direct evidence for the formation of Cr(V). Kinetic measurements were consistent with the role of Cr(V) and H2O2 as intermediates in .OH formation. These results indicate that in cellular media, especially during chromate phagocytosis, the O-2 radical can become a significant source of .OH radicals and hence a significant factor in the biochemical mechanism of cellular damage due to Cr(VI) exposure.
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PMID:The role of superoxide radical in chromium (VI)-generated hydroxyl radical: the Cr(VI) Haber-Weiss cycle. 130 99

Evidence for the generation of superoxide anion in an enzymatic action of tyrosinase is reported. In the dopatyrosinase reaction, 1 mol of O2 is required for the production of 2 mol of dopaquinone, 1 mol of dopachrome, and 1/4 mol of O2-. Superoxide dismutase and 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (a chemiluminescence probe and O2 trap) do not inhibit the rate of dopachrome formation from dopa in the presence of tyrosinase, indicating that free O2- is not utilized for metabolizing dopa. ESR studies for the accumulation of semiquinone radicals generated from tyrosine and N-acetyltyrosine in the presence of tyrosinase imply that O2- is not generated by the semiquinone + O2 reaction. Since the addition of H2O2 and dopa to tyrosinase promotes the release of O2- and formation of dopachrome, the Cu(II)O2-Cu(I) complex could be formed as a intermediate (an active form of tyrosinase); [Cu(II)]2 + H2O2 in equilibrium Cu(I)O2-Cu(II) + 2H+.
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PMID:Generation of superoxide during the enzymatic action of tyrosinase. 130 77

Using ESR, a radical (g = 2.004) was detected in the reaction mixture of 3-hydroxykynurenine (3-HKY), H2O2, and horseradish peroxidase. The radical was stable and was detected even after 5 h. On HPLC analysis of the reaction mixture, two radical peaks (Peak-1 and Peak-2) were detected using ESR. The ESR spectra of Peak-1 and Peak-2 radicals were the same and identical with that of the original radical in the reaction mixture. The retention times of Peak-1 and Peak-2 corresponded to those of authentic xanthommatin (XA) and hydroxanthommatin (Hydro-XA), respectively, XA being formed in the oxidation of 3-HKY by potassium ferricyanide and Hydro-XA being formed in the reduction of XA by sodium metabisulfite. The absorbance spectra of Peak-1 and Peak-2 were nearly identical with those of authentic XA and Hydro-XA. The absorbance spectrum of Peak-2 changed from that of Hydro-XA to that of XA, indicating that Hydro-XA auto-oxidized to XA in the air. The ESR signal intensity of the Peak-2 radical developed in accordance with the progress of this auto-oxidation of Hydro-XA to XA. It was supposed that the Peak-2 radical was generated in the auto-oxidation of Hydro-XA after its elution from the HPLC column. Thus, the radical seemed to be the one-electron oxidized form of Hydro-XA. The Peak-1 radical appeared to be the true retention of the radical on the column and to be eluted with a much larger amount of XA. The separation of the radical from XA was impossible on the column. Hemoglobin (Hb) or hematin also induced the same radical in the reaction mixture of 3-KHY, H2O2, and Hb or hematin.
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PMID:Formation of hydroxanthommatin-derived radical in the oxidation of 3-hydroxykynurenine. 131 47

The oxidation of NADH and accompanying reduction of oxygen to H2O2 stimulated by polyvanadate was markedly inhibited by SOD and cytochrome c. The presence of decavanadate, the polymeric form, is necessary for obtaining the microsomal enzyme-catalyzed activity. The accompanying activity of reduction of cytochrome c was found to be SOD-insensitive and therefore does not represent superoxide formation. The reduction of cytochrome c by vanadyl sulfate was also SOD-insensitive. In the presence of H2O2, all the forms of vanadate were able to oxidize reduced cytochrome c, which was sensitive to mannitol, tris and also catalase, indicating H2O2-dependent generation of hydroxyl radicals. Using ESR and spin trapping technique only hydroxyl radicals, but not superoxide anion radicals, were detected during polyvanadate-dependent NADH oxidation.
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PMID:Characterization of oxygen free radicals generated during vanadate-stimulated NADH oxidation. 131 4

The widely used food additives butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) react with oxyhemoglobin, thereby forming methemoglobin. The reaction rates were measured using visible spectroscopy, and second order rate constants were established for BHA and compared with p-hydroxyanisole. Using ESR we investigated the involvement of free radical reaction intermediates. The expected one-electron oxidation product of BHA and BHT, the phenoxyl radical, could only be detected with pure 3-t-butyl-4-hydroxyanisole and oxyhemoglobin. With the commercial mixture of 2- and 3-t-butyl-4-hydroxyanisole a very strong ESR signal of a secondary free radical species was observed, similar to the one observed earlier with p-hydroxyanisole and dependent on the presence of free thiol groups, so that we assumed the intermediate existence of a perferryl species, the MetHb-H2O2 adduct. In a second series of experiments we investigated the reactivity of this postulated intermediate with BHA and BHT, starting with a pure MetHb/H2O2-phenol mixture in a stopped-flow apparatus linked to the ESR spectrometer, detecting the expected phenoxyl radicals from BHA and p-hydroxyanisole. Due to the low solubility and decreased reactivity of BHT only traces of phenoxyl type radical were found together with a high concentration of unreacted perferryl species. The reactivity of BHA, BHT and p-hydroxyanisole with free thiol groups is demonstrated by an increased reaction rate in the presence of the thiol group blocking substance NEM.
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PMID:Methemoglobin formation from butylated hydroxyanisole and oxyhemoglobin. Comparison with butylated hydroxytoluene and p-hydroxyanisole. 131 49

In the presence of hydrogen peroxide (H2O2), xanthine oxidase has been found to catalyze sulfur trioxide anion radical (SO3.-) formation from sulfite anion (SO3(2-)). The SO3.- radical was identified by ESR (electron spin resonance) spin trapping, utilizing 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) as the spin trap. Inactivated xanthine oxidase does not catalyze SO3.- radical formation, implying a specific role for this enzyme. The initial rate of SO3.- radical formation increases linearly with xanthine oxidase concentration. Together, these observations indicate that the SO3.- generation occurs enzymatically. These results suggest a new property of xanthine oxidase and perhaps also a significant step in the mechanism of sulfite toxicity in cellular systems.
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PMID:Xanthine oxidase/hydrogen peroxide generates sulfur trioxide anion radical (SO3.-) from sulfite (SO3(2-)). 131 48

The formation of hydroxyl radicals (.OH) by the reaction of CuII(edta) (edta: ethylenediaminetetraacetic acid) with hydrogen peroxide (H2O2) in the presence of biological reductants, such as L-ascorbic acid and L-cysteine, has been demonstrated for the first time by ESR spectroscopy using water-soluble spin-traps, 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 1), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN, 2) and 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 3). Ethylenediaminetetraacetic acid (edta) is one of the polyamine-N-polycarboxylate chelating agents and it is commonly used by chemists and biochemists. Edta can chelate several metal ions. It is known that the CuII(edta) complex is usually less active than free copper ions in radical reactions, whereas complexes of edta with Fe(II) or Fe(III) still react with hydrogen peroxide (H2O2) or superoxide ion (O2-) (1). In our previous papers (2-4), we also have shown that copper(II) complexes with polyamine-N-polycarboxylates, such as edta and dtpa (diethylenetriaminepentaacetic acid), do not react with H2O2, whereas CuII(en)2 (en: ethylenediamine) can easily do so to give hydroxyl radical (.OH) as a reactive intermediate. Further, we assumed that the change of redox potential of Cu(II) ions as a result of ligation with different ligands causes the difference in reactivity of Cu(II) complexes towards H2O2. To verify this assumption, the reactions of CuII(edta), which was chosen as a Cu(II)-polyamine-N-polycarboxylate complex, with H2O2 were investigated in the presence of some biological reductants, using an ESR-spin trapping method.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Reactions of copper(II)-N-polycarboxylate complexes with hydrogen peroxide in the presence of biological reductants: ESR evidence for the formation of hydroxyl radical. 132 Aug 83

Reaction of elemental copper and zinc powder mixtures with glycine (NH2.CH2COOH; HA) or aspartic acid (NH2CHCOOHCH2COOH; H2B) (in 1:1:2 ratio, respectively) in the presence of excess hydrogen peroxide (H2O2) at 50 degrees C, results in the formation of a new mixed metal peroxy carbonate compound corresponding to formula [Cu(Zn)2(O2(2-) (CO3)2(H2O)4], while the same reaction with elemental copper powder alone yields merely peroxy amino acid compounds having the formula [Cu(O2(2-)) (HA)2(H2O)] and [Cu(O2(2-)) (H2B) (H2O)2] for glycine and aspartic acid, respectively. These compounds have been characterized by elemental analysis, ESR, and electronic and IR spectra. It is interesting to note that both amino acids are converted to carbonate in the presence of zinc alone. A method analogous to that described above, for the reaction of elemental copper, zinc powder mixtures with succinic acid [(CH2COOH)2] or acetic acid (CH3COOH) in excess H2O2, on the other hand, gave a product essentially comprising copper succinate or acetate, respectively. These observations suggest an interesting and perhaps important phenomenon by which only the simple amino acids such as glycine and aspartic acid are converted to carbonates while their corresponding carboxylic acids form only their respective salts.
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PMID:Effect of zinc ion on the interaction of some amino acid compounds of copper(II) with hydrogen peroxide. 132 85

Transition metal ions, especially iron, appear to be important mediators of oxidative damage in vivo. Iron(II) reacts with H2O2 to give more-reactive radicals. On the basis of ESR spin-trapping data with DMPO, supported by aromatic hydroxylation studies and patterns of DNA base modification, it is concluded that hydroxyl radical (OH.) is likely to be the major damaging species formed in Fenton Systems under biologically-relevant conditions (which include iron concentrations no higher than the micromolar range). Although reactive oxo-iron species (such as ferryl and perferryl) may also be important, direct chemical evidence for their formation and identity in biologically relevant Fenton systems is currently lacking. Studies at alkaline pH values show that iron(IV) and iron(V) species are highly oxidizing under those reaction conditions, with a pattern of reactivity different from that of OH..
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PMID:Biologically relevant metal ion-dependent hydroxyl radical generation. An update. 132 23

The effect of the general anaesthetic propofol (2,6-diisopropylphenol) on lipid peroxidation in rat liver mitochondria was assessed with the thiobarbituric acid (TBA) assay. Propofol was shown to inhibit the accumulation of TBA-reactive compounds after initiation of radical production by the addition of the ADP-Fe2+ complex. Analysis of kinetics showed that propofol caused a concentration-dependent delay as well as a decrease in the rate of the peroxidation process. 1H-NMR spectra of mitochondrial lipid extracts indicated that 95% of the added propofol remained intact after 30 min incubation under conditions of low oxidative stress. The ESR spectrum of propofol incubated in the presence of EDTA-Fe2+ and H2O2 as initiators of radical production showed a radical that was most likely a decomposition product of the primary phenoxy radical of propofol. It is concluded that (a) propofol acts as a chain reaction-breaking antioxidant by forming a stable radical and (b) propofol does not seem to be metabolized in mitochondria in vitro.
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PMID:Inhibition of lipid peroxidation in isolated rat liver mitochondria by the general anaesthetic propofol. 132 68


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