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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Citrate-Fe3+, reportedly a physiological chelate, exhibits superoxide dismutaselike activity, as evidenced by the inhibition of xanthine oxidase-dependent cytochrome c reduction; the dismutation of xanthine oxidase-generated superoxide to hydrogen peroxide and oxygen, and the enhanced disproportionation of potassium superoxide. The catalytic activity of citrate-Fe3+ corresponds, on a molar basis, to 0.03% of that of copper- and zinc-containing superoxide dismutase. Although weak, this activity enables citrate-Fe3+ to inhibit superoxide and ADP-Fe3+ -dependent peroxidation of extracted microsomal lipids. Also, the dismutase activity of citrate-Fe3+ interferes with its ability to promote lipid peroxidation. It is proposed that chelation of Fe3+ by citrate may represent a protective mechanism against the deleterious consequences of superoxide generation.
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PMID:Superoxide-dependent redox cycling of citrate-Fe3+: evidence for a superoxide dismutaselike activity. 302 73

When Chinese hamster fibroblasts were exposed to hydrogen peroxide or to a system consisting of xanthine oxidase and hypoxanthine, which generates superoxide anion plus hydrogen peroxide, sister-chromatid exchanges (SCEs) were formed in a dose-dependent manner. When the iron-complexing agent o-phenanthroline was present in the medium, however, the production of these SCEs was completely inhibited. This fact indicates that the Fenton reaction: Fe2+ + H2O2----OH0 + OH- + Fe3+ is responsible for the production of SCEs. When O2- and H2O2 were generated inside the cell by incubation with menadione, the production of SCE was prevented by co-incubation with copper diisopropylsalicylate, a superoxide dismutase mimetic agent. The most likely role of O2- is as a reducing agent of Fe3+: O2- + Fe3+----Fe2+ + O2, so that the sum of this and the Fenton reaction, i.e., the iron-catalyzed Haber-Weiss reaction, provides an explanation for the active oxygen species-induced SCE: H2O2 + O2(-)----OH- + OH0 + O2. According to this view, the OH radical thus produced is the agent which ultimately causes SCE. These results are discussed in comparison with other mechanisms previously proposed for induction of SCE by active oxygen species.
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PMID:Iron-mediated induction of sister-chromatid exchanges by hydrogen peroxide and superoxide anion. 303 88

Haemocuprein was discovered fifty years ago by T. Mann and D. Keilin as a copper protein of red blood cells, later named erythrocuprein. Superoxide dismutase was discovered twenty years ago by J.M. McCord and I. Fridovich as an enzymatic activity in preparations of carbonic anhydrase or myoglobin that inhibited the aerobic reduction of cytochrome c by xanthine oxidase. Astonishingly the superoxide dismutase proved to be haemocuprein. Around this time zinc was found in haemocuprein, in equimolar amount to the copper. Haemocuprein thus became copper-zinc superoxide dismutase after thirty years as an obscure cuproprotein of red blood cells. This historical article is a tribute to the achievement of J.M. McCord and I. Fridovich. Their discovery of superoxide dismutase revolutionized the study of oxygen free-radicals in biochemistry.
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PMID:From haemocuprein to copper-zinc superoxide dismutase: a history on the fiftieth anniversary of the discovery of haemocuprein and the twentieth anniversary of the discovery of superoxide dismutase. 306 13

An automated enzymatic method is described for the determination of Cu,Zn-superoxide dismutase (SOD) in plasma or erythrocytes using the xanthine-xanthine oxidase and cytochrome C coupled assay. This method was adapted to an Abbott ABA-200 discrete analyzer. Coefficients of variation for within-run and day-to-day analyses were less than 5%. Only 2.5 muL of serum or erythrocyte extract is required so a capillary tube sample of blood (70 muL) is sufficient for the assay. Recovery of added SOD ranged from 92 to 101%. The method reported here is practical for use in a clinical chemistry laboratory for monitoring changes in this enzyme, which is a sensitive early indicator of alterations in copper status.
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PMID:An automated method for the determination of Cu,Zn-superoxide dismutase in plasma and erythrocytes using an ABA-200 discrete analyzer. 308 43

Male C57Bl/10 mice were chronically fed hexachlorobenzene (HCB) (0.02% of the diet) alone or in combination with a single subcutaneous dose of iron (12.5 mg iron per mouse). After eight weeks the group of mice pretreated with the iron overload was highly sensitized to the porphyrogenic effect of HCB, as shown by liver porphyrin accumulation. A synergistic effect of iron was evident on other parameters too, such as HCB-induced hepatic damage, activation of type O of xanthine oxidase, and decreased activity of copper zinc superoxide dismutase and glutathione peroxidase(s). None of these parameters was affected by iron alone. Iron alone and in association with HCB markedly raised the level of lipid peroxides, the increase in the HCB group being smaller. The combined treatment resulted in a significant reduction of HCB's inductive effects on microsomal heme and cytochromes P-450 and b5 and on the activity of aryl hydrocarbon hydroxylase. The content of nonprotein sulfhydryl groups was reduced to the same extent in mice treated with HCB or HCB plus iron. The results suggest that reactive intermediates such as are formed by lipid peroxidation are not sufficient on their own to create the conditions for uroporphyrinogen decarboxylase impairment, as evident in the group of mice receiving iron overload alone. Conversely, HCB administration induced a specific condition of imbalance in the liver between formation and inactivation of reactive intermediates which was associated with hepatic porphyrin accumulation and was potentiated by concomitant administration of iron.
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PMID:Investigations on the role of free radical processes in hexachlorobenzene-induced porphyria in mice. 323 39

The depletion of superoxide dismutase in the liver of rats held on a copper-deficient diet for 8 weeks induces two profound modifications in microsomal membrane characteristics. These membranes show: (1) a low degree of peroxidation induced in vitro by both endogenous (NADPH and tert-butylhydroperoxide) and exogenous sources (xanthine/xanthine oxidase) of oxygen radicals as revealed by malondialdehyde and diene-conjugate production; (2) a strong decrease of polyunsaturated and an increase of monounsaturated fatty acid content. These alterations are similar to those found in microsomal membranes from fast-growing hepatomas which exhibit a pronounced saturation of fatty acid pattern and lack superoxide dismutase. These observations support the hypothesis that during hepatocarcinogenesis the loss of superoxide dismutase causes an oxidative stress that increases cellular membrane lipid peroxidation, as a consequence of which the cell responds by synthesizing more saturated fatty acids that permanently modify cell membrane structure and properties.
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PMID:Superoxide dismutase depletion and lipid peroxidation in rat liver microsomal membranes: correlation with liver carcinogenesis. 340 6

The abilities of pig liver (copper, zinc) metallothionein I and rat liver zinc metallothionein II to modify lipid peroxidation in incubations of liver microsomes have been compared with the activities of reduced glutathione, mannitol, quinacrine, EDTA, dimethyl-pyrroline-N-oxide and phenyl-butyl-nitrone. Lipid peroxidation was determined by assay of thiobarbituric acid reactive substance formation in incubations of microsomes with iron/ADP or a mixture of xanthine and xanthine oxidase. Zinc metallothionein II had no effect on the extent of peroxidation in either system but (copper, zinc) metallothionein I caused a stimulation of peroxidation initiated by xanthine and xanthine oxidase, all other compounds tested were inhibitory. Gel exclusion chromatography of incubations of (copper, zinc) metallothionein I with xanthine and xanthine oxidase revealed aggregation of the metalloprotein. This may have exposed copper in a form capable of initiating peroxidation.
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PMID:Stimulation of peroxidation in rat liver microsomes by (copper, zinc)-metallothioneins. 350 92

Extracellular-superoxide dismutase is a tetrameric enzyme containing four copper atoms. It has previously been shown to catalyse the decay of the superoxide radical, but the resulting product was not determined. In a xanthine oxidase-xanthine system in which about 30% of the electron flux resulted in superoxide radical formation, accumulation of hydrogen peroxide was determined. Catalysis of superoxide radical decay by extracellular-superoxide dismutase was found to result in hydrogen peroxide formation. The catalysed reaction is thus identical to those of previously investigated superoxide dismutases. Human manganese superoxide dismutase was also found to dismute the superoxide radical to hydrogen peroxide and water.
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PMID:Product of extracellular-superoxide dismutase catalysis. 383 41

1. The ;xanthine oxidase' activity of rat liver supernatant, most of which behaves as an NAD(+)-dependent dehydrogenase (type D) can be rapidly converted into an oxidase (type O) by thiol reagents such as tetraethylthiuram disulphide, copper sulphate, 5,5'-dithiobis-(2-nitrobenzoic acid), N-ethylmaleimide and p-hydroxymercuribenzoate. Treatment with copper sulphate, if prolonged, leads to almost complete inactivation of the enzyme. The effect of these reagents is prevented by dithioerythritol, and in all cases but that of N-ethylmaleimide is reversed by the same thiol. 2. Dithioerythritol prevents and reverses the conversion of xanthine oxidase from type D into type O brought about by storage of rat liver supernatant at -20 degrees C, preincubation under anaerobic conditions, treatment with carbon or with diethyl ether, and reverses, but does not prevent, the conversion obtained by preincubation of the whole liver homogenate. 3. Conversion of the enzyme from type D into type O is effected by preincubation of rat liver supernatant with the sedimentable fraction from rat liver but not from chick or pigeon liver. The xanthine dehydrogenase activity of chick liver supernatant is not changed into an oxidase by preincubation with the sedimentable fraction from rat liver. 4. The enzyme activity of rat liver supernatant is converted from type D into type O during purification of the enzyme: the purified enzyme can be reconverted into type D by dithioerythritol. 5. The enzyme appears as an oxidase in the supernatant of rat heart, intestine, spleen, pancreas, lung and kidney. The enzyme of all organs but intestine can be converted into a dehydrogenase by dithioerythritol.
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PMID:The regulation of rat liver xanthine oxidase. Involvement of thiol groups in the conversion of the enzyme activity from dehydrogenase (type D) into oxidase (type O) and purification of the enzyme. 434 95

Vegetative and reproductive cells of Basidiobolus haptosporus possess naturally occurring organelles identified as microbodies. Cells of four other species of the genus contained morphologically indistinguishable organelles. Microbodies were invariably present in cells of the fungi grown on routine mycological media. The constitutive microbody was characterized by a single, intensely electron-opaque crystalloid body which rapidly enlarged to fill the organellar compartment. The microbody then underwent degeneration by an autolytic-like process. Growth of the fungi on xanthine and its catabolites as sole nitrogen sources (but not urea) greatly enhanced the production of new microbodies in which protein was initially accumulated as paracrystalline arrays. These inclusions then underwent reorganization and compaction to form crystalloid bodies. Key enzymes of the purine degradation pathway are believed to be core proteins of the crystalloid. D-amino acid oxidase, alpha-hydroxy acid oxidase, xanthine oxidase and urate oxidase (but not catalase) were detected cytochemically in mature microbodies. Significant levels of phosphorus and molybdenum were present in the microbody crystalloid by X-ray dispersive microanalysis; iron and copper were not detected. The ability of Basidiobolus species to assimilate xanthine and its catabolites might explain their ecological association with the gut and cloacal contents of various amphibia, reptiles and fish.
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PMID:Ultrastructural cytology of Basidiobolus haptosporus: morphology and electron cytochemistry of microbodies. 615 82


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