Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study looks at the role of xanthine oxidase (XO) in ischemia/reperfusion (I/R) induced intestinal mucosal damage using normal and xanthine oxidase deficient rats. Tungstate feeding for 3 days depleted the intestinal mucosal XO by 80%. A ligated loop of the rat small intestine (both normal and XO-deficient) was subjected to 1 h of total ischemia followed by 5 min revascularisation. The ensuing mucosal damage was assessed by biochemical and histological studies. Ischemia or I/R increased the XO levels in normal rats without any change in XO-deficient rats. Myeloperoxidase (a neutrophil marker) level was increased in both group of rats but it was comparatively higher in the XO-deficient rats. Accumulation of peroxidation products such as malondialdehyde, conjugated diene and increased production of hydroxyl radicals by microsomes were seen after ischemia and I/R and were similar in normal and XO-deficient rats. Studies on other parameters of peroxidation showed a decrease in polyunsaturated fatty acids and alpha-tocopherol, an increase in cysteine and cystine levels after I/R and were similar in both normal and XO-deficient rats. Histological results indicated gross morphological changes in the intestinal mucosa due to ischemia and I/R, and the damage was more severe in XO-deficient rats. These observations suggest that oxygen-derived free radicals are involved in the intestinal mucosal damage during I/R and infiltrated neutrophils rather than XO may be the primary source of free radicals under these conditions.
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PMID:Oxygen free radical induced damage during intestinal ischemia/reperfusion in normal and xanthine oxidase deficient rats. 823 77

We isolated cDNAs encoding xanthine dehydrogenase (XD; xanthine:NAD+ oxidoreductase, EC 1.1.1.204) from a human liver cDNA library. The complete nucleotide sequence of human XD was determined; the deduced amino acid sequence encoded a protein of 1336 amino acid residues of M(r) 147,782. Human XD possessed many of the signature sequences typical of XDs from flies and rodents, including an unusual cysteine distribution, a potential 2Fe/2S binding site, and a putative molybdopterin cofactor binding domain. Analysis of potential NAD binding sites suggested a simple hypothesis for the conversion of human XD into the oxygen metabolite forming xanthine oxidase (XO; xanthine:oxygen oxidoreductase, EC 1.1.3.22). Using a human XD complementary RNA hybridization probe, we found a 5100-base RNA in human liver by RNA blot-hybridization analysis. This RNA exhibited tissue-specific distribution that may be pertinent to XD- and XO-mediated oxygen radical injury in ischemia/reperfusion and inflammation. A second 4500-base RNA was detected in some tissues and may arise through differential transcription termination.
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PMID:cDNA cloning, characterization, and tissue-specific expression of human xanthine dehydrogenase/xanthine oxidase. 824 61

Binding of [3H]serotonin and of [3H]dopamine to serotonin binding proteins (SBP) from soluble extracts of bovine frontal cortex is increased by Fe2+ but not by Fe3+. It was generally believed that Fe2+ first binds to sulfhydryl groups of SBP and that the monoamines form coordination bonds with the trapped iron. We report two series of findings that are incompatible with this mechanism. First, the binding of both radioligands is an irreversible process since it is not diminished when a large excess (1 mM) of serotonin or dopamine is added to a pre-equilibrated mixture of SBP, 0.1 mM Fe2+ and 0.2 microM radioligand. Once formed, binding is not impaired by chelating agents such as ethyleneglycoltetraacetic acid and desferal. Second, the Fe(2+)-stimulated binding is inhibited by reducing agents (sodium ascorbate, vitamin E, sodium metabisulfite) and by agents which deplete superoxide radicals (superoxide dismutase and hydrogen peroxide). Moreover, the effect of Fe2+ can be mimicked by oxidants (sodium periodate, potassium superoxide) and by the generation of superoxide radicals by the xanthine oxidase-catalysed oxidation of xanthine. To integrate these findings, we formulate the hypothesis that Fe2+ reacts with dissolved molecular oxygen to produce superoxide radicals, that these radicals oxidise [3H]serotonin and [3H]dopamine, and that the formed oxidation products bind covalently to cysteine residues of SBP. This alternative mechanism is also based on the ability of reagents which contain or modify sulfhydryl groups to decrease the binding and on the inability of hydroxyl radical scavengers (dimethyl sulfoxide, mannitol, ethanol and thiourea) to do so. Fe2+ is also able to irreversibly inactivate part of the binding sites on SBP (81% of the specific binding of [3H]serotonin, and 61% for [3H]dopamine). This Fe(2+)-mediated inactivation, as well as the covalent nature of the binding, preclude the interpretation of saturation and competition binding data in terms of reversible bimolecular interactions. Yet, such experiments indicate that, at the same concentration, [3H]dopamine binds to 2 to 3 times more sites than [3H]serotonin. Unlabelled dopamine acts also as a potent competitor at all the [3H]serotonin binding sites, whereas unlabelled serotonin only acts as a potent competitor at part (30%) of the [3H]dopamine binding sites. SBP were initially proposed to be involved in the storage, protection and/or transport of serotonin, and recently also of catecholamines. However, these potential functions of SBP can hardly be reconciled with the molecular mechanism of the binding. Moreover, it is conceivable that this binding actually represents an in vitro model for neurodegeneration.
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PMID:Binding of serotonin and dopamine to 'serotonin binding proteins' in bovine frontal cortex: evidence for iron-induced oxidative mechanisms. 825 56

The anti-oxidative effects of R8605, a compound of the third generation retinoids, have been studied. R8605 exhibited pronounced inhibitory effects on FeSO4/cysteine and NADPH/vitamin C-induced lipid peroxidation of rat liver microsome as well as on H2O2-induced lipid peroxidation of erythrocytes: Their IC50's were 9.8, 17.6 and 20.3 mumol/L, respectively. R8605 decreased the generation of superoxide anion (O2-.) in a xanthine/xanthine oxidase system and also elevated hepatic superoxide dismutase (SOD) activity in mice. Therefore R8605 shows potent antioxidative effects and this is likely of importance in its chemopreventive actions.
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PMID:[Anti-oxidative effects of R8605, a third-generation retinoid]. 832 39

We investigated whether captopril, an angiotensin-converting enzyme (ACE) inhibitor with a sulfhydryl group, enalaprilat, an ACE inhibitor without a sulfhydryl group, and cysteine, an amino acid with a sulfhydryl group but no ACE-inhibiting properties, could scavenge hydrogen peroxide and prevent oxidant-induced cell injury. When 0.1-2.5 mM concentrations of captopril, cysteine, or enalaprilat were incubated with xanthine oxidase and hypoxanthine for 0-120 min, the recovery of hydrogen peroxide was significantly (P < 0.001) reduced in the presence of captopril or cysteine, whereas enalaprilat had no effect on the recovery of hydrogen peroxide. Captopril and cysteine could not scavenge hydrogen peroxide when the sulfhydryl group was blocked with N-ethylmaleimide. When human renal tubular epithelial cells and human umbilical vein endothelial cells were exposed to hydrogen peroxide, oxidant-induced depletion of ATP and efflux of [3H]adenine metabolites was mildly reduced in the presence of captopril or cysteine but was not altered by enalaprilat. Cysteine was more effective in preventing oxidant-induced cell injury than captopril. We conclude that because of its sulfhydryl group, captopril at millimolar concentrations can scavenge hydrogen peroxide and can slightly reduce, but does not eliminate, oxidant-induced cell injury.
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PMID:Captopril scavenges hydrogen peroxide and reduces, but does not eliminate, oxidant-induced cell injury. 838

Toward the development of a fluorescence assay in combination with confocal microscopy to image free radicals generated by cells, we synthesized a fluorophore-nitroxide, 5-((2-carboxy)phenyl)-5-hydroxy-1-((2,2,5,5-tetramethyl-1-oxypyrrolid in-3- yl)methyl)-3-phenyl-2-pyrrolin-4-one sodium salt, and tested the applicability of this probe to detect oxygen-centered free radicals. The reaction of the fluorophore-nitroxide with superoxide (10 microM/min) generated either by the reaction of xanthine oxidase on xanthine or by PMA-activated neutrophils in the presence of cysteine (200 microM) resulted in a loss of electron spin resonance (ESR) signal intensity concurrent with an increase in fluorescence emission. The decrease in ESR signal and the augmentation in fluorescence emission were inhibited by the addition of superoxide dismutase. This fluorophore-nitroxide also reacted with methyl radical generated by the reaction of hydroxyl radical with DMSO (0.14 M). In this case a loss in ESR signal intensity concomitant with an increase in fluorescence emission which were inhibited by catalase (300 U/ml), was recorded. These results clearly demonstrated the feasibility of using fluorescence methodology in conjunction with a fluorophore-nitroxide to detect oxygen-centered free radicals in biological systems.
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PMID:A fluorophore-containing nitroxide as a probe to detect superoxide and hydroxyl radical generated by stimulated neutrophils. 839 65

Bovine lens aldose reductase (alditol: NADP+ oxido-reductase, EC 1.1.1.21) undergoes a thiol-dependent oxidative modification catalyzed by the Fe(II)/Fe(III) redox system. The enzyme is inactivated by various oxygen radical generating systems. However, addition of 2-mercaptoethanol to the oxygen radical generating systems resulted in an initial increase followed by a decrease in the activity of aldose reductase. The net maximal increase in the enzyme activity was observed with 3 mM 2-mercaptoethanol, 0.3 mM FeSO4, and 0.9 mM EDTA, either with or without 1 mM hypoxanthine and 37 mU/ml of xanthine oxidase. The formation of the stable, activated intermediate, ARa, appears to proceed through the reaction between the enzyme and the oxidized form of 2-mercaptoethanol which in the presence of iron, forms a mixed disulfide with a cysteine residue. Reduction of ARa with dithiothreitol released 0.7 mol of 2-mercaptoethanol per mole of enzyme and converted it to a form that resembled the native aldose reductase.
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PMID:Thiol-dependent metal-catalyzed oxidation of bovine lens aldose reductase. I. Studies on the modification process. 842 75

Active oxygen species are generated during pathophysiologic conditions such as inflammation and ionizing radiation exposure. We tested the hypothesis that an early cellular event in response to these species involves regulation of ion channels. We exposed cells to gamma-irradiation or treated them with hydrogen peroxide, xanthine/xanthine oxidase, or [3H]thymidine and then monitored channel activity by the technique of whole-cell voltage clamping. Recordings showed that both normal and tumor cells exhibit an increase in K+ currents after treatment with radiation, H2O2, and xanthine/xanthine oxidase but not with high specific activity [3H]thymidine, suggesting that the signal for K+ channel activation originates at the cell membrane. A single noncytotoxic dose of 10 cGy induced measurable levels of K+ currents, suggesting that the induction of currents regulates biochemical changes in response to stress. To test whether channel activity is sensitive to active oxygen species, we pretreated cells with N-acetyl-L-cysteine (NAC) to increase cellular pools of free radical scavengers before radiation. In NAC-pretreated cells, K+ channel activation by gamma-irradiation was abolished. It has previously been shown that protein kinase C (PKC) is activated by ionizing radiation and can regulate K+ channels in some cells. However, the effect of radiation on induction of K+ channel activity was independent of PKC, since cells chronically exposed to phorbol esters still produced K+ currents after radiation. These results suggest that an early cellular response to oxidative stress is the activation of K+ channels.
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PMID:Potassium-channel activation in response to low doses of gamma-irradiation involves reactive oxygen intermediates in nonexcitatory cells. 843 Jan 4

The effects of systems generating active oxygen species (superoxide anion, hydrogen peroxide, hydroxyl radical) on tyrosinase have been studied in cultured human melanoma cells. Tyrosinase activity was determined by measuring the quantity of 5-S-L-cysteinyl-L-dopa (5-S-CD) formed in the presence of D,L-dopa and L-cysteine. In some experiments, the enzyme protein was determined by radio immunoassay [RIA]. Exposure of cells to xanthine/xanthine oxidase or glucose/glucose oxidase resulted in a dose-related elevation of tyrosinase. Catalase, but not superoxide dismutase, prevented this increase indicating that hydrogen peroxide may be the agent responsible for the action, whereas superoxide anion is not involved. Hydroxyl radicals formed by the Haber-Weiss or Fenton type reactions were not found to produce elevation of tyrosinase. Catalase determinations showed no enzyme in the medium but a high concentration in the cells. Inhibition of intracellular catalase by 3-amino-1,2,4-triazole caused an increase in the tyrosinase level. The effects of dopac, xanthine/xanthine oxidase, and glucose/glucose oxidase all producing hydrogen peroxide, and increasing tyrosinase, were enhanced by the inhibition of catalase. It is concluded that hydrogen peroxide, formed by the systems, accounts for the elevation of tyrosinase level. When tyrosinase activities determined by 5-S-CD formation were compared to enzyme amounts found by RIA, the ratios of these values were always constant. This fact indicates that the increase in the tyrosinase activities was not due to an activation of the enzyme, but mirrored the quantities of enzyme protein present in the samples. On the basis of our findings, it is assumed that hydrogen peroxide is a regulator of tyrosinase in normal melanocytes and melanoma cells.
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PMID:Hydrogen peroxide as an inducer of elevated tyrosinase level in melanoma cells. 843 9

The gastric epithelium is exposed to oxygen radicals that are generated within the lumen. Much interest has been focused on the role of mucus in maintaining integrity of the gastric mucosa against oxidants, because gastric mucus may act as a scavenger of oxygen radicals. The aim of this study was to assess the role of mucous glycoprotein in protecting cultured gastric epithelial cells against oxygen radicals. Monolayer cultures of rat gastric mucus-producing cells were studied. Oxygen radicals were generated by hypoxanthine and xanthine oxidase. Cytotoxicity was quantified by measuring chromium 51 release form prelabeled cells. Rate of mucous synthesis was estimated by incorporation of tritiated glucosamine into the cells. The effects of tetraprenyl acetone (a stimulant of mucus production) and N-acetyl-L-cysteine (a mucolytic agent) on oxygen radical-induced damage were determined. Preincubation with tetrapenyl acetone, while stimulating mucous glycoprotein by the cultured cells, caused a dose-dependent reduction of hypoxanthine-xanthine oxidase-induced 51Cr release, reaching maximum protection of the damage by 31% to 50%. In contrast, pretreatment with N-acetyl-L-cysteine potentiated oxygen radical-induced 51Cr release dose dependently. The protective effect of tetraprenyl acetone was significantly abolished by N-acetyl-L-cysteine. Neither tetraprenyl acetone nor N-acetyl-L-cysteine alone under the conditions of this study affected the cellular content of glutathione, which modulates oxygen radical injury to these cells. These results suggest that mucous glycoprotein partially but significantly protects cultured gastric epithelial cells against extracellularly generated oxygen radicals. It seems likely, therefore, that gastric mucus is involved in antioxidant defenses in these cells.
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PMID:Role for mucous glycoprotein in protecting cultured rat gastric mucosal cells against toxic oxygen metabolites. 845 39


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