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)

A group of substituted 5,8-quinolinequinones which exhibit antineoplastic activity and which are structurally related to the antitumor antibiotic streptonigrin induce single strand cleavage of PM2 covalently-closed circular-DNA (ccc-DNA) when reductively activated. The cleavage which is detected by an ethidium fluorescence assay is specifically enhanced by cuprous and ferrous ion and is selectively inhibited by superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) and by free radical scavengers. Independent generation of the superoxide ion by xanthine-xanthine oxidase (EC 1.2.3.2) also cleaves PM2 DNA and therefore a chemical mechanism for the scission process induced by the streptonigrin analogues is formulated. A correlation between rate of PM2 ccc-DNA cleavage and inhibition of Walker carcinosarcoma 256 is observed.
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PMID:Studies related to antitumor antibiotics. Part VIII. Cleavage of DNA by streptonigrin analogues and the relationship to antineoplastic activity. 127 71

SR 4233 (3-amino-1,2,4-benzotriazine-1,4-dioxide) is a novel benzotriazine di-N-oxide which shows unusually high selective toxicity towards hypoxic cells, probably as a result of reductive bioactivation. Using an HPLC assay for the parent drug and its 2- and 4-electron reduction products (SR 4317 and SR 4330, respectively), we have examined the enzymology of SR 4233 reductive metabolism in vitro using a variety of different enzyme preparations. SR 4233 was converted extremely rapidly to SR 4317 under N2 by mouse liver microsomes, and showed a marked preference for NADPH over NADH as a reduced cofactor. The reaction was inhibited completely in air and boiled preparations. It was also inhibited by 78-86% in carbon monoxide (CO), implicating cytochrome P-450 as the major microsomal SR 4233 reductase. The kinetics of reductive metabolism of SR 4233 to SR 4317 by mouse liver microsomes conformed to Michaelis-Menten kinetics, with a Km of 1.4 mM and a Vmax of 950 nmol/min/mg protein. SR 4233 reduction was also catalysed by mouse liver cytosol under N2. However, rates were markedly slower than for microsomes and showed an equal dependency on NADH and NADPH. The cytosolic enzymes aldehyde oxidase and xanthine oxidase both catalysed SR 4233 reduction to SR 4317 under N2. Purified buttermilk xanthine oxidase also catalysed this reaction. In contrast to other enzyme preparations, DT-diaphorase from Walker 256 tumour cells reduced SR 4233 predominantly to SR 4330, and this reaction occurred under aerobic conditions. These data illustrate that SR 4233 is reduced rapidly by a wide variety of reductases. We propose that the therapeutic selectivity of SR 4233 will be controlled by the relative expression of reductases in tumour versus normal tissues, and in particular by the differential participation of putative activating versus detoxifying enzymes.
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PMID:Enzymology of the reductive bioactivation of SR 4233. A novel benzotriazine di-N-oxide hypoxic cell cytotoxin. 234 70

The passage of circulating tumor cells across vessel walls is an important step in cancer metastasis and is promoted by endothelial injury. Because Walker carcinosarcoma 256 (W256) cells generate oxygen-derived free radicals after cellular activation, the authors tested the hypothesis that these cancer cells can damage endothelial monolayers by producing such reactive oxygen species. To confirm that oxygen-derived radicals can damage endothelial cells, 3H-2-deoxyglucose-labeled human endothelial cell monolayers were exposed to xanthine oxidase in the presence of 0.2 mmol/l xanthine. 3H-2-deoxyglucose release was observed after the addition of xanthine oxidase in concentrations ranging from 6.5 x 10(-3) to 52 x 10(-3) units/ml. The extent of damage correlated with xanthine oxidase-dependent chemiluminescence (r = 0.91). Chemiluminescence assays in the presence of 5 x 10(-5) M luminol confirmed activation of the W256 cells by 1 x 10(-6) M chemotactic peptide fMLP. When fMLP-activated activated W256 cells were incubated with endothelial monolayers, concentrations of 2 x 10(6) to 6 x 10(6) W256 cells/ml were found to cause a 27% increase in the specific release of 2-deoxyglucose after a 90-minute incubation. A small but significant increase in 3H-2-deoxyglucose release also was observed in the absence of fMLP. Detection of 3H-2-deoxyglucose release in the presence of activated or unactivated tumor cells was dependent on preincubating the endothelial cell monolayer with 1 mM buthionine sulfoximine, an inhibitor of glutathione synthesis. Under these conditions, the specific release of 3H-2-deoxyglucose was increased from nondetectable levels to 21%, in the presence of 6.5 x 10(-3) units of the oxidase. Cultured W256 cells promoted isotope release from endothelial cell monolayers when activated with phorbol myristate acetate. Catalase (1000 units/ml) inhibited the tumor cell-induced release of 3H-2-deoxyglucose by 84% whereas superoxide dismutase, even at concentrations of 1 mg/ml, had no effect. A requirement for cell contact was shown because addition of cell-free supernatants from fMLP activated tumor cells did not cause 3H-2-deoxyglucose release and because pretreatment of W256 cells with 1 microM cytochalasin B inhibited their ability to promote isotope release even while increasing tumor cell-generated chemiluminescence threefold. Electron microscopy revealed that fewer cytochalasin B-treated W256 cells were attached to the endothelial cell monolayer than in untreated controls. It is concluded that the W256 tumor cells can damage endothelial cells directly via a mechanism involving production of reactive oxygen species.
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PMID:Walker carcinosarcoma cells damage endothelial cells by the generation of reactive oxygen species. 270 6

The toxic effect and anti-tumor activity of B-3839, a new molecular combination of pyrimidine antimetabolite 5-fluorouracil (5-FU) with the alkylating agent N-Chloroethyl-N-nitrosourea (BCNU), was compared to that of BCNU and 5-FU given alone and in physical combination. The tumor inhibitory effect of B-3839 was similar to that of BCNU given alone or combined with a low dose of 5-FU in the i.m. Walker tumor model. Furthermore, the bone marrow toxicity of BCNU was not significantly altered by either form of combination with 5-FU. The intestinal side effects, evaluated by measuring the decrease of marker enzyme (thymidine kinase, xanthine oxidase, alkaline phosphatase, sucrase, maltase) activities in isolated enterocytes, were dose-dependent and moderate. A significant, more than 30%, decrease occurred only if BCNU and 5-FU were given simultaneously or as B-3839. The molecular combination of the two drugs does not provide any additional advantage over their physical combination.
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PMID:Comparison of tumor growth inhibitory and toxic effects of a new fluorouracil--nitrosourea derivative (B-3839). 297 32

We tested the hypothesis proposed by Topham, Woodruff and Walker that intestinal xanthine oxidase is important for iron absorption. We made weanling rats xanthine oxidase-deficient and measured their growth and iron status. There were no significant differences between control and xanthine oxidase-depleted rats in growth or iron absorption or a variety of measures of iron metabolism, except that xanthine oxidase-depleted rats accumulated nonheme iron in the liver. Iron deficiency caused a loss in intestinal xanthine oxidase activity, but also caused an increase in hepatic xanthine oxidase activity. This result may be important for understanding changes in purine and protein metabolism during iron deficiency.
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PMID:Effect of molybdenum-deficient and low iron diets on xanthine oxidase activity and iron status in rats. 654 77

Isolated from bovine milk, xanthine oxidase (XO) and xanthine dehydrogenase (XDH) are two interconvertible forms of the same protein, differing in the number of protein cysteines versus cystines. Most differences between XO and XDH are localized to the FAD center, the site at which the oxidizing substrates NAD and molecular oxygen react. A comparative study of the reduction of XO and XDH has been performed to assess differences in reactivity of the molybdopterin site, as well as subsequent electron-transfer events from molybdenum to 2Fe/2S and FAD centers. The compound 4-hydroxypyrimidine (4-OH-P) was chosen as reducing substrate because its higher Km value raised the possibility of binding weak enough to measure kinetically, and its high kcat value could allow detection of intramolecular electron-transfer reactions. As measured by stopped flow spectrophotometry, XO and XDH react with the first equivalent of 4-OH-P via similar mechanisms, differing in the magnitude of rate and dissociation constants. Using [2-2H]4-OH-P as substrate, a D(k/Kd) isotope effect of 1.9 to 2.3 suggests that movement of the hydrogen abstracted from substrate appreciably limits the rate of initial enzyme reduction from Mo(VI) to Mo(IV). Monitoring the visible spectrum of the enzymes, the first observed step is reduction of a single 2Fe/2S center and presumably re-oxidation of Mo(IV) to Mo(V). This suggests a common pathway for electron transfer involving reduction of a 2Fe/2S center prior to reduction of the second 2Fe/2S and FAD centers. Rates of the first electron transfer from molybdenum to the 2Fe/2S center are rapid, 290 s-1 with XO and 180 s-1 with XDH, and are consistent with rates measured by flash photolysis (Walker, M. C., Hazzard, J. T., Tollin, G., and Edmondson, D. E. (1991) Biochemistry 30, 5912-5917) allowing discrete observation of the electron-transfer reactions that occur during turnover. This step also exhibits a modest primary kinetic isotope effect of 1.5 to 1.6 when [2-2H]4-OH-P is used, possibly due to deprotonation of the molybdenum center prior to electron transfer. A second one-electron transfer, presumably oxidizing Mo(V) to Mo(VI), follows in a step coincident with product dissociation, consistent with a role for product release in controlling electron transfer events. The kinetics of this complex system are described and interpreted quantitatively in models that are consistent with all the data.
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PMID:Kinetic isotope effects and electron transfer in the reduction of xanthine oxidoreductase with 4-hydroxypyrimidine. A comparison between oxidase and dehydrogenase forms. 927 4