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)

Normal tissue toxicity of nitroaromatic radiosensitizers may originate in radiosensitizer/nitroreductase interaction. A study of two mammalian cell nitroreductases, xanthine oxidase and NADH cytochrome c reductase, shows that the efficiency of electron transfer is dependent on sensitizer electron affinity and not lipid solubility. Misonidazole and its demethylated metabolite (RO-05-9963), for example, are equally efficient as electron acceptors from xanthine oxidase. The only exception to the electron affinity correlation is m-nitrobenzamidine hydrochloride (MNBAM) which results because MNBAM inhibits electron donation to xanthine oxidase from its cofactor, xanthine. Allopurinol inhibits electron transfer and might be a useful adjuvant to the use of radiosensitizers. Evidence that allopurinol interacts with nitroreductases in vivo is deduced from the observation that allopurinol significantly alters the serum lifetimes in mice of misonidazole and RO-05-9963.
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PMID:Structure-function dependence and allopurinol inhibition of radiosensitizer/nitroreductase interaction: approaches to improving therapeutic ratios. 677 Oct 29

The activation of N2-methyl-9-hydroxyellipticinium acetate (4) by a peroxidase--H2O2 system leads to the formation of an omicron-quinone (7a). This omicron-quinone is not directly generated from the starting material but through a quinone imine intermediate (6) which is subsequently oxidized. This reaction is highly dependent on pH values. The omicron-quinone 7a is easily protonated (7b), gives an addition product with methanol (9), and is reduced by cysteine. The omicron-quinone 7b has a rather low inhibitory effect against L1210 leukemia cell multiplication but acts as an electron carrier and dramatically augments the oxygen consumption in xanthine oxidase-NADH and rat liver microsomes-NADPH systems.
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PMID:omicron-Quinone formation in the biochemical oxidation of the antitumor drug N2-methyl-9-hydroxyellipticinium acetate. 683 91

The inhibition of the activity of xanthine oxidase by vanadate was strikingly similar to vanadate inhibition of another molybdoprotein nitrate reductase. Although the main catalytic activity of both enzymes was inhibited, the partial NADH oxidase activity associated with these enzymes was stimulated several fold. It appears that the metal ion binds at multiple site in both enzymes. In the absence of any enzymes a combination of vanadium (V) and molybdenum (V) in air was found to oxide NADH rapidly.
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PMID:Effects of vanadate on the molybdoproteins xanthine oxidase and nitrate reductase: kinetic evidence for multiple site interaction. 689 79

The catalytic oxidation of [14C]-formate to 14CO2 was adapted to measure H2O2 formation in cellfree system. Standard curves employing glucose-glucose oxidase and xanthine-xanthine oxidase demonstrated linearity between 14CO2 evolution and enzyme concentration. A particulate fraction from human neutrophils was capable of oxidizing [14C]-formate; this reaction was dependent upon the presence of catalase, reduced pyridine nucleotide, and cellular material. Reaction increased with time of incubation and protein concentration, although not in a strictly linear fashion. The pH optimum was approximately 5.5 NADPH was a significantly better substrate than NADH, although both were capable of generating H2O2. The particulate fraction derived from phagocytizing cells was more active than a corresponding fraction from resting cells with either substrate. H2O2 production was abnormal in particulate fractions derived from 2 patients with chronic granulomatous disease. H2O2 production was markedly inhibited by superoxide dismutase or cytochrome c (scavengers of superoxide anion) but not by scavengers of singlet oxygen or hydroxyl radical. Reaction was greatly stimulated by the addition of manganous ion. These results are consistent with the hypothesis that the respiratory burst in human neutrophils is initiated by an oxidase that can utilize either NADPH or NADH but exhibits a marked preference for the former. Further, the inhibitor studies strongly support a mechanism involving an initial enzymatic reaction followed by a self-sustaining free radical reaction involving superoxide anion.
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PMID:Pyridine nucleotide-dependent generation of hydrogen peroxide by a particulate fraction from human neutrophils. 689 95

The electron transfer mechanism in the reduction of aromatic nitro compounds by xanthine oxidase was investigated using methyl p-nitrobenzoate and p-nitroacetophenone as substrates. Methyl p-nitrobenzene was reduced by both one-electron and more than two-electron transfer mechanisms in the enzyme-electron donor system. When NADH was used as an electron donor, the ratio of one-electron flux to the total electron flux (the summation of one-electron and more than two-electron fluxes) was dependent on pH of the medium, but not on the concentration of the nitro compounds. The reverse was the case when the electron donor was xanthine. Additional experiments showed that methyl p-nitrobenzoate or p-nitroacetophenone was reduced to the corresponding hydroxylamino compounds and amino compounds by xanthine oxidase supplemented with xanthine or NADH. In these cases, the pattern of formation of the reduction products was dependent on the enzyme activity. The present study strongly suggested that the reduction of aromatic nitro compounds by xanthine oxidase proceeds through the four-electron and six-electron transfer mechanisms as well as the one-electron transfer mechanism.
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PMID:Mode of reactions between xanthine oxidase and aromatic nitro compounds. 689 90

Metallothionein inhibited in a concentration-dependent fashion the reduction of nitroblue tetrazolium [NBT] mediated by xanthine oxidase and by NADH-phenazine methosulfate. This catalytic activity of metallothionein for dismutation of O2- is dependent on the copper content in metallothionein.
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PMID:Inhibition of nitroblue tetrazolium reduction by metallothionein. 689 6

Superoxide radicals were investigated as to their capability of depolymerizing the hyaluronic acid of the bovine vitreous body. Using viscometry it was found that O2 radicals, generated by the hypoxanthine/xanthine oxidase method or the combination of NADH and phenazine methosulphate, degraded hyaluronic acid. This reaction was suppressed by superoxide dismutase, catalase, and peroxidase. In contrast, the depolymerization of hyaluronic acid by oxidation-reduction systems like ascorbic acid or ferrous ions was abolished by catalase and peroxidase while superoxide dismutase showed no effect.
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PMID:The inability of superoxide dismutase to inhibit the depolymerization of hyaluronic acid by ferrous ions and ascorbate. 690 74

The course of the reaction sequence hypoxanthine leads to xanthine leads to uric acid, catalysed by the NAD+-dependent activity of xanthine oxidoreductase, was investigated under conditions either of immediate oxidation of the NADH formed or of NADH accumulation. The enzymic preparation was obtained from rat liver, and purified 75-fold (as compared with the 25000 g supernatant) on a 5'-AMP-Sepharose 4B column; in this preparation the NAD+-dependent activity accounted for 100% of total xanthine oxidoreductase activity. A spectrophotometric method was developed for continuous measurements of changes in the concentrations of the three purines involved. The time course as well as the effects of the concentrations of enzyme and of hypoxanthine were examined. NADH produced by the enzyme lowered its activity by 50%, resulting in xanthine accumulation and in decreases of uric acid formation and of hypoxanthine utilization. The inhibition of the Xanthine oxidoreductase NAD+-dependent activity by NADH is discussed as a possible factor in the regulation of IMP biosynthesis by the 'de novo' pathway or (from unchanged hypoxanthine) by ther salvage pathway.
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PMID:Effect of NADH on hypoxanthine hydroxylation by native NAD+-dependent xanthine oxidoreductase of rat liver, and the possible biological role of this effect. 695 74

When xanthine oxidase was prepared from fresh raw cow's milk in the presence of dithioerythritol, 94% of its xanthine-oxidizing activity was found as a dehydrogenase type. The enzyme was reversibly converted to an oxidase type when dithioerythritol was removed. The conversion was ascribable to the oxidation of sulfhydryl groups of the enzyme by oxygen. The two forms of the enzyme gave the same visible spectrum, but the dehydrogenase form alone gave a characteristic difference spectrum upon addition of NAD+. NADH served as a good electron donor for the dehydrogenase form of the enzyme but not for the oxidase form. When xanthine was used as an electron donor, the overall rate of p-benzoquinone reduction was the same for the oxidase and dehydrogenase forms, but the proportion of one-electron flux from the enzyme to p-benzoquinone was considerably greater in the reaction of the dehydrogenase form than in that of the oxidase form.
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PMID:Preparation of bovine milk xanthine oxidase as a dehydrogenase form. 695 93

Xanthine oxidase (xanthine:O2 oxidoreductase, EC 1.2.3.2) was purified from bovine milk lipid globules to electrophoretic homogeneity (Mr 155,000) and antibodies were raised against it in rabbits. By immunolocalization techniques, the xanthine oxidase antigen was detected in milk lipid globules and mammary gland epithelium, but also in capillary endothelium from various tissues, including liver, lung and intestine. These findings were paralleled by measurements of xanthine oxidase activities in the tissues, both in a membrane-associated and a soluble form. Addition of hypoxanthine to fractions containing native xanthine oxidase did not promote lipid peroxidation, in contrast to the widely used in vitro system for lipid peroxidation which involves addition of xanthine oxidase preparations. Extraction with buffers of high ionic strength and with nonionic detergents removed only part of the enzyme from the membranes. Immunoprecipitates from the soluble supernatant fractions, using anti-xanthine oxidase IgG, were enriched in the Mr 155,000 polypeptide. Patterns of proteolytic cleavage products of the xanthine oxidase monomer from capillaries and milk lipid globules were similar but not identical. Immunoprecipitates from soluble fractions of milk lipid globules and tissues were enriched in both xanthine oxidase and NADH-cytochrome c reductase activities. Electrophoretic separation of proteins from milk lipid globule membranes under non-denaturing conditions revealed a close correlation of xanthine oxidase and part of the NADH-cytochrome c reductase activity, but showed different activity profiles of NADH-ferricyanide reductase and xanthine oxidase.
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PMID:Characteristics of membrane-bound and soluble forms of xanthine oxidase from milk and endothelial cells of capillaries. 703 83


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