Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Isolated erythrocyte membranes exposed to protease-free xanthine oxidase plus xanthine and ferric iron undergo lipid peroxidation and protein crosslinking (appearance of high molecular weight aggregates on sodium dodecyl sulfate (SDS) gel electrophoresis). Spectrin is more susceptible to crosslinking than the other polypeptides. Thiol-reducible bonds (disulfides) as well as nonreducible bonds are generated, the former type relatively rapidly (detected within 10-20 min) and the latter type more slowly (usually detected after 1 h). Reducible crosslinking is inhibited by catalase, but not by superoxide dismutase, desferrioxamine, butylated hydroxyltoluene, and mannitol; whereas nonreducible crosslinking, like free radical lipid peroxidation, is inhibited by all of these agents except mannitol. Zinc(II) also inhibits lipid peroxidation, but stimulates disulfide bond formation to the virtual exclusion of all other crosslinking. Our results indicate that disulfide formation is dependent on H2O2, but not O2- or iron. However, O2-, H2O2, and iron are all required for lipid peroxidation and nondisulfide crosslinking, suggesting the intermediacy of OH generated via the iron-catalyzed Haber-Weiss reaction. The possible role of malonaldehyde (MDA, a by-product of lipid peroxidation) in the latter type of crosslinking was examined. Solubilized samples of xanthine/xanthine oxidase-treated membranes showed a strong visible fluorescence (emission maximum 450 nm; excitation 390 nm). This resembled the fluorescence of membranes treated with authentic MDA, which forms conjugated imine linkages between amino groups. Fluorescence scanning of SDS gels from MDA-treated membranes showed a strong signal coincident with crosslinked proteins and also one in the low molecular weight, nonprotein region, suggestive of aminolipid conjugates. Similar scanning on xanthine/xanthine oxidase-reacted membranes indicated that all fluorescence is associated with the lipid fraction. Thus, nonreducible protein crosslinks in this system do not appear to be of the MDA-derived, Schiff base type.
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PMID:Xanthine oxidase-catalyzed crosslinking of cell membrane proteins. 380 Mar 91

Xanthine oxidase and xanthine, a combination that produces hydrogen peroxide and superoxide anion radical, applied topically in anesthetized cats equipped with cranial windows caused arteriolar dilation during application, sustained dilation 1 h after washout, and reduced reactivity to the vasoconstrictive effects of arterial hypocapnia, discrete lesions of the endothelium, and morphological abnormalities of the vascular smooth muscle by electron microscopy. Similar effects were seen in small, but not in large, arterioles during topical application of hydrogen peroxide or hydrogen peroxide plus ferrous sulfate, a combination that produces free hydroxyl radical. The functional changes caused by xanthine oxidase plus xanthine were inhibited completely by superoxide dismutase plus catalase. Superoxide dismutase or catalase, each by itself, eliminated the residual effects seen after washout and reduced the dilation during application of xanthine oxidase. The results show that superoxide anion radical and hydrogen peroxide produce reversible arteriolar dilation and that consistent vascular damage is produced in the presence of both superoxide anion radical and hydrogen peroxide.
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PMID:Effects of oxygen radicals on cerebral arterioles. 391 62

Superoxide (.O-2) is demonstrated to participate at the prostaglandin phase swelling (2-4 h) of carrageenan paw edema. Superoxide production is inhibited in vitro by typical anti-inflammatory drugs, but these drugs did not scavenge superoxide which was produced by xanthine oxidase. Phosphate, pyrophosphate, ATP, ADP and sulfate were essential for superoxide production by macrophages. These anions can induce paw swelling and are reported to increase in rheumatic patients. A mixture of macrophages and lymphocytes from BCG sensitized guinea-pigs was cultured for 2 days with SOD or D-mannitol. Nitroblue tetrazolium reduction (formazan formation) was inhibited by these agents, suggesting that the hydroxyl radical (.OH) is necessary for metabolic activation of macrophage. Lympholine-like factor of which production or release is enhanced by hydroxyl radical, activates macrophage. Production of oxygen radicals may increase rapidly by this chain cycle reaction. Possible relations of oxygen radicals to prostaglandin(s) biosyntheses, chemotaxis, lysosomal enzyme release protease participation, were discussed. Endogenous SOD, epinephrine, ceruloplasmin, blood plasma proteins, inflammatory fluid, may modulate the amount of superoxide by their superoxide scavenging capacities.
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PMID:Inflammation and superoxide production by macrophages. 626 69

Activation of the desulfo forms of milk xanthine oxidase, chicken liver xanthine dehydrogenase, and aldehyde oxidase with S2- is greatly facilitated in the presence of reducing agents. Upon anaerobic incubation with 1 mM S2- and 1 mM dithionite, desulfo xanthine oxidase and chicken liver xanthine dehydrogenase prepared by cyanide treatment of active enzymes, are activated to the specific activity predicted by their molybdenum content. Routine preparations containing desulfo molecules are also similarly activated to the extent predicted. Cyanide-inactivated chicken liver xanthine dehydrogenase was reconstituted with 35S2- in the presence of dithionite. 85% of enzyme-bound radioactivity was shown to be in the form of cyanolyzable sulfur, by comparison of enzyme activity, bound radioactivity, and 35SCN- yields from exposure of labeled enzyme to cyanide. This radiolabeled enzyme allowed the determination of the following. 1) The cyanolyzable sulfur is largely removed from the polypeptide by incubation at 37 degrees C for one hour in 1% sodium dodecyl sulfate, pH 7, or for 15 min in 6 M guanidinium chloride, pH 6.2. 2) The cyanolyzable sulfur is "acid labile." [35S]Methylene blue is formed in the theoretical quantity from oxidized or substrate-reduced enzyme under the standard conditions for labile sulfur analysis by the methylene blue method. These data strongly support the conclusion that the cyanolyzable sulfur is a terminal sulfur ligand of the Mo atom, and is not part of an organic moiety.
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PMID:Evidence for the inorganic nature of the cyanolyzable sulfur of molybdenum hydroxylases. 627 83

Uninduced rat liver microsomes and NADPH-Cytochrome P-450 reductase, purified from phenobarbital-treated rats, catalyzed an NADPH-dependent oxidation of hydroxyl radical scavenging agents. This oxidation was not stimulated by the addition of ferric ammonium sulfate, ferric citrate, or ferric-adenine nucleotide (AMP, ADP, ATP) chelates. Striking stimulation was observed when ferric-EDTA or ferric-diethylenetriamine pentaacetic acid (DTPA) was added. The iron-EDTA and iron-DTPA chelates, but not unchelated iron, iron-citrate or iron-nucleotide chelates, stimulated the oxidation of NADPH by the reductase in the absence as well as in the presence of phenobarbital-inducible cytochrome P-450. Thus, the iron chelates which promoted NADPH oxidation by the reductase were the only chelates which stimulated oxidation of hydroxyl radical scavengers by reductase and microsomes. The oxidation of aminopyrine, a typical drug substrate, was slightly stimulated by the addition of iron-EDTA or iron-DTPA to the microsomes. Catalase inhibited potently the oxidation of scavengers under all conditions, suggesting that H2O2 was the precursor of the hydroxyl radical in these systems. Very high amounts of superoxide dismutase had little effect on the iron-EDTA-stimulated rate of scavenger oxidation, whereas the iron-DTPA-stimulated rate was inhibited by 30 or 50% in microsomes or reductase, respectively. This suggests that the iron-EDTA and iron-DTPA chelates can be reduced directly by the reductase to the ferrous chelates, which subsequently interact with H2O2 in a Fenton-type reaction. Results with the reductase and microsomal systems should be contrasted with results found when the oxidation of hypoxanthine by xanthine oxidase was utilized to catalyze the production of hydroxyl radicals. In the xanthine oxidase system, ferric-ATP and -DTPA stimulated oxidation of scavengers by six- to eightfold, while ferric-EDTA stimulated 25-fold. Ferric-desferrioxamine consistently was inhibitory. Superoxide dismutase produced 79 to 86% inhibition in the absence or presence of iron, indicating an iron-catalyzed Haber-Weiss-type of reaction was responsible for oxidation of scavengers by the xanthine oxidase system. These results indicate that the ability of iron to promote hydroxyl radical production and the role that superoxide plays as a reductant of iron depends on the nature of the system as well as the chelating agent employed.
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PMID:The role of iron chelates in hydroxyl radical production by rat liver microsomes, NADPH-cytochrome P-450 reductase and xanthine oxidase. 633 21

The effects of topical application of agents which produce oxygen radicals on cerebral arterioles were studied in anesthetized cats. Xanthine oxidase plus xanthine, which produced superoxide anion radical, hydrogen peroxide, and hydrogen peroxide plus ferrous sulfate, which produced the free hydroxyl radical, induced sustained dilation, reduced responsiveness to the vasoconstrictor effect of hypocapnia, and destructive lesions of the endothelium and of the vascular smooth muscle. Similar effects were produced by arachidonate, 15-HPETE, and PGG2. The effect of arachidonate was inhibited by mannitol, a free hydroxyl radical scavenger, the effect of PGG2 was inhibited by SOD, the effect of 15-HPETE was inhibited by either catalase or SOD. These results suggest that these cerebral vascular abnormalities were produced by a single destructive free radical, probably the hydroxyl free radical, generated via interaction of superoxide and hydrogen peroxide. Cerebral vascular abnormalities similar to those produced by oxygen radicals were also seen after experimental concussive brain injury or after acute hypertension. After brain injury, activation of phospholipase C and increased brain prostaglandin concentration were demonstrated. The vascular effects of brain injury and acute hypertension were inhibited by free radical scavengers. The results suggest that, in these conditions, vascular damage is induced by oxygen radicals generated from arachidonate in association with increased prostaglandin synthesis.
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PMID:Oxygen radicals and vascular damage. 640 99

We have examined the effects of folate compounds and the folate analog amethopterin (methotrexate) as inhibitors of mammalian xanthine oxidase and have found that they offer potent inhibition of the enzyme. We have compared the inhibitory potency of folic acid and its coenzyme derivative tetrahydrofolic acid to that of allopurinol, a known inhibitor of xanthine oxidase, and have demonstrated that folic acid and tetrahydrofolic acid are severalfold more potent than allopurinol as inhibitors of xanthine oxidase. Comparative inhibition constants calculated were 5.0 X 10(-7) M for folic acid. 1.25 X 10(-6) M for tetrahydrofolic acid, and 4.88 X 10(-6) M for allopurinol. Incubation of xanthine oxidase with folic acid at a concentration of 10(-6) M abolished 94% of the enzymic activity within 1 min of incubation with the enzyme. At the same concentration, allopurinol was almost ineffective as an inhibitor of xanthine oxidase. The substrate xanthine protected the enzyme against total inhibition by folic acid. Reversibility of the enzymic inhibition by folic acid was demonstrated. Folic acid-inactivated enzyme was totally regenerated either by filtration through Sephadex G-200 or by precipitation with ammonium sulfate. 2-Amino-4-hydroxypteridine was a poor substrate for the enzyme but a potent inhibitor for the oxidation of xanthine by the enzyme. The inhibition constant calculated was 1.50 X 10(-6) M. In the presence of an excess of xanthine oxidase, neither folic acid nor tetrahydrofolic acid and allopurinol exhibited any change in intensity of their absorbance or in the wavelength of their maximal absorbance that might have been suggestive of substrate utility. The folate analog amethopterin was also determined a potent inhibitor of mammalian xanthine oxidase. The inhibition constant calculated was 3.0 X 10(-5) M.
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PMID:Inhibition of mammalian xanthine oxidase by folate compounds and amethopterin. 660 20

The microsomal oxidation of ethanol or 1-butanol was increased by ferrous ammonium sulfate-ethylenediaminetetraacetic acid (1:2) (Fe-EDTA) (3.4-50 microM). The increase was blocked by hydroxyl radical scavenging agents such as dimethyl sulfoxide or mannitol. The activities of aminopyrine demethylase or aniline hydroxylase were not affected by Fe-EDTA. The accumulation of H2O2 was decreased in the presence of Fe-EDTA, consistent with an increased utilization of H2O2. Other investigators have shown that Fe-EDTA increases the formation of hydroxyl radicals in systems where superoxide radicals are generated. The stimulation by Fe-EDTA appears to represent a pathway involving hydroxyl radicals rather than catalase because (1) stimulation occurred in the presence of azide, which inhibits catalase, (2) stimulation occurred in the presence of 1-butanol, which is not an effective substrate for catalase, and (3) stimulation was blocked by hydroxyl radical scavenging agents, which do not affect catalase-mediated oxidation of ethanol. A possible role for contaminating iron in the H2O or buffers could be ruled out since similar results were obtained with or without chelex-100 treatment of these solutions. The stimulatory effect by Fe-EDTA required microsomal electron transfer with NADPH, and H2O2 could not replace the NADPH-generating system. In the absence of microsomes or catalase, Fe-EDTA also stimulated the coupled oxidation of ethanol during the oxidation of xanthine by xanthine oxidase. These results suggest that during microsomal electrom transfer, conditions may be appropriate for a Fenton type or a modified Haber-Weiss type of reaction to occur, leading to the production of hydroxyl radicals.
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PMID:Role of hydroxyl radicals in the iron-ethylenediaminetetraacetic acid mediated stimulation of microsomal oxidation of ethanol. 677 47

Purified liver microsomal NADPH-cytochrome P-450 reductase is able to catalyze the activation of [14C]ronidazole to metabolite(s) which bind covalently to protein. Like the reaction catalyzed by microsomes, protein alkylation catalyzed by the reductase is (1) sensitive to oxygen, (2) requires reducing equivalents, (3) is inhibited by sulfhydryl-containing compounds and (4) is stimulated several fold by either flavin mononucleotide (FMN) or methytlviologen. A cytochrome P-450 dependent pathway of ronidazole activation can be demonstrated as judged by the inhibition of the reaction by carbon monoxide, metyrapone and 2,4-dichloro-6-phenylphenoxyethylamine but the involvement of specific microsomal cytochrome P-450 isozymes has not been definitively established. Milk xanthine oxidase is also capable of catalyzing ronidazole activation. Polyacrylamide sodium dodecyl sulfate (SDS)-gel electrophoresis reveals that the reactive intermediate(s) of ronidazole does not alkylate proteins selectively.
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PMID:Drug residue formation from ronidazole, a 5-nitroimidazole. II. Involvement of microsomal NADPH-cytochrome P-450 reductase in protein alkylation in vitro. 680 46

A procedure has been developed to distinguish between the two forms of eukaryotic superoxide dismutases using a common activity assay. Treatment of cellular fractions with 2% sodium dodecyl sulfate at 37 degrees C for 30 min selectively inactivates the mitochondrial, manganese-containing variant without affecting the cytosolic copper, zinc-superoxide dismutase. After removing excess sodium dodecyl sulfate by precipitation with potassium chloride, the supernate is assayed using the xanthine oxidase-cytochrome c method.
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PMID:A method for distinguishing Cu,Zn- and Mn-containing superoxide dismutases. 684 3


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