UNIPROT:P47989 - FACTA Search

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

The behavior of the rate-limiting enzyme of purine catabolism, xanthine oxidase (EC 1.2.3.2); was examined in normal liver, in 17 hepatomas of different growth rates, and in rapidly growing differentiating and regenerating liver. Xanthine oxidase activity was measured in the supernatant fluid prepared by centrifugation of 5% homogenates at 100,000 X g for 30 min. There was no uricase activity in the supernatant fluid. The affinity of xanthine oxidase to xanthine was similar in normal liver and in slow- and rapidly growing hepatomas (Km=6 to 8 muM), and theoptimum pH was 8.0; at pH 7.4, the activity was 80% of that at the pH optimum. A standard assay was worked out for the liver and hepatoma systems; the enzyme activity was linear during 60-min incubation and proportionate with amounts of protein added over a range of 0.5 to 3.0 mg. Xanthine oxidase specific activity was 9 times higher in small intestine than in liver. Activities in lung, spleen, kidney, heart, testes, and thymus were 67, 59, 21, 19, 8, and 8%, and in skeletal muscle, brain, and bone marrow activities were 5% of that of the liver. In regenerating liver, xanthine oxidase activity was not changed from that of the liver of sham-operated controls up to 96 hr after operation. The activity of the average differentiating liver cell was less than 5% of that of adult liver during the first week after birth. At postnatal ages of 18, 25, 30 and 40 days, the activity rose to 18, 46, 76, and 94%, respectively, of that of the adult liver. In starvation, hepatic xanthine oxidase activity per cell was preferentially depleted as compared to the decline in protein concentration. Upon refeeding, the enzymatic activity was restored more slowly than the protein content. Since xanthine oxidase activity was decreased in all examined hepatomas, including the slowest-growing, well-differentiated neoplasms, the altered activity of this enzyme appears to be.linked with neoplastic transformatiobosyl 1-pyrophosphate amidotransferase (EC 2.4.2.14), was increassed in the hepatomas, the reprogramming of gene expression results in an imbalance that favors the synthetic over the catabolic potential. This enzymatic imbalance should confer selective advantages to the cancer cells.
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PMID:Imbalance of purine metabolism in hepatomas of different growth rates as expressed in behavior of xanthine oxidase (EC 1.2.3.2). 18 29

DNA adduct formation in the liver of B6C3F1 mice after administration of 1-nitropyrene (1-NP) was shown by the 32P-postlabeling technique. The major adduct was not N-(deoxyguanosin-8-yl)-1-aminopyrene, which was easily formed in in vitro nitroreduction of 1-NP in the presence of DNA, but the major spots migrated to the same position as the in vitro DNA adduct spots of K-region epoxides of 1-NP (1-NP 4,5- and 9,10-oxide). 1-NP oxides formed by the oxidative activation of 1-NP in the liver were excreted into the bile as detoxified glutathione conjugates which were changed to cysteine conjugates in the upper intestinal tract. The cysteine conjugates were degraded by cysteine conjugate beta-lyase (beta-lyase) of intestinal microflora in the lower intestinal tract. The mutagenicity of cysteine conjugates of 1-NP oxides for Salmonella typhimurium was enhanced by addition of beta-lyase and was decreased by addition of aminooxyacetic acid, a beta-lyase inhibitor. The in vitro binding of the cysteine conjugates to calf thymus DNA was increased by addition of beta-lyase and xanthine oxidase. We administered glutathione conjugates of 1-NP oxides to two groups of mice that had been treated with antibiotics or saline by gavage and analyzed the DNA adducts in the lower intestinal mucosa. The specific DNA adducts were detected in the saline-treated group but not in the antibiotics-treated group. These results suggest that intestinal microflora play an important role in activation of glutathione conjugates of 1-NP oxides.
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PMID:Role of intestinal microflora in metabolism of glutathione conjugates of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide. 130 95

1. The mutagenicity of 1-nitropyrene metabolites in Chinese hamster ovary (CHO) cells, in the absence of rat liver S9, decreased in the order 6-hydroxy-1-nitropyrene > 1-nitropyrene 9,10-oxide > 1-nitropyrene 4,5-oxide approximately 3-hydroxy-1-nitropyrene approximately 8-hydroxy-1-nitropyrene > 1-nitropyrene. The order of mutagenicity with rat liver S9 was 1-nitropyrene 4,5-oxide approximately 6-hydroxy-1-nitropyrene approximately 1-nitropyrene 9,10-oxide > 3-hydroxy-1-nitropyrene approximately 1-nitropyrene > 8-hydroxy-1-nitropyrene. 2. 1-Nitropyrene 4,5-oxide reacted with calf thymus DNA to give one or several closely related adducts. The same adducts were detected in CHO cells incubated with 1-nitropyrene 4,5-oxide. Inclusion of a nitroreductase, xanthine oxidase, in the incubations with calf thymus DNA resulted in the formation of an additional adduct identified as N-(deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP). 3. 1-Nitropyrene 9,10-oxide reacted with calf thymus DNA to give an adduct pattern similar to that observed with 1-nitropyrene 4,5-oxide. Incubation of 1-nitropyrene 9,10-oxide with CHO cells resulted in the formation of the same adducts along with dG-C8-AP. 4. dG-C8-AP and N-(deoxyguanosin-8-yl)-1-amino-x-nitropyrene (x = 3, 6 or 8; dG-C8-ANP) were detected in injection site DNA from Sprague-Dawley rats treated with 1-nitropyrene. In mammary gland DNA, dG-C8-AP and an unidentified adduct were found. dG-C8-ANP was the only DNA adduct detected in the livers of newborn CD-1 mice and the lungs of A/J mice dosed with 1-nitropyrene.
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PMID:Metabolic activation of 1-nitropyrene to a mammalian cell mutagen and a carcinogen. 144 3

The metabolism and DNA adduct formation by the mutagenic environmental contaminant 2-nitrofluoranthene (2-NFA) were studied. Incubation under aerobic conditions with liver microsomes of rats pretreated with 3-methylcholanthrene yielded trans-7,8-dihydroxy-7,8-dihydro-2-nitrofluoranthene, trans-9,10-dihydroxy-9,10-dihydro-2-nitrofluoranthene, and 7-, 8-, and 9-phenolic metabolites. When the epoxide hydrolase inhibitor 3,3,3-trichloropropylene was present in the incubation, only phenolic metabolites were detected. Under hypoxic conditions, 2-aminofluoranthene was obtained, together with a trace of the ring-oxidized metabolites. The activated metabolite, N-hydroxy-2-aminofluoranthene, was prepared in situ and reacted with calf thymus DNA. Upon enzymatic hydrolysis of the DNA and purification by HPLC, a C8-substituted deoxyguanosine adduct, N-(deoxyguanosin-8-yl)-2-aminofluoranthene, was identified by mass and proton NMR spectral analysis. This adduct was also formed at a level of 10 pmol/mg of DNA when 2-NFA was metabolized by xanthine oxidase, 6 pmol/mg of DNA from incubation with liver microsomes of rats pretreated with 3-methylcholanthrene, and 3-pmol/mg of DNA from metabolism by liver microsomes of rats pretreated with phenobarbital.
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PMID:In vitro metabolism and DNA adduct formation from the mutagenic environmental contaminant 2-nitrofluoranthene. 148 38

Aristolochic acid II (AAII), one of the major components of the carcinogenic plant extract aristolochic acid, is known to be mutagenic and to form DNA adducts in vitro and in vivo. The major fluorescent DNA adduct formed upon xanthine oxidase mediated reduction in the presence of calf thymus (CT-) DNA or deoxyadenosine was isolated by means of preparative HPLC and identified by fluorescence, UV/vis absorbance, and 1H NMR spectroscopy as 7-(deoxy-adenosin-N6-yl)aristolactam II. As a model proximate carcinogen, N-chloroaristolactam II was prepared chemically from aristolactam II, the reduction product of AAII. This model compound was spectroscopically characterized and found to react directly with CT-DNA without any activation, forming the same deoxyadenosine adduct. HPLC analysis with fluorescence monitoring detected this adduct in vivo in the liver DNA of Wistar rats treated orally with AAII. These results confirm the anticipated metabolic activation mechanism of AAII as occurring via a cyclic nitrenium ion.
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PMID:N6-adenyl arylation of DNA by aristolochic acid II and a synthetic model for the putative proximate carcinogen. 166 54

Nitrated polycyclic aromatic hydrocarbons are wide-spread environmental pollutants that have been detected in photocopier toners, airborne particulates, coal fly ash, and diesel engine exhaust emissions. 1-Nitropyrene, a representative nitropolycyclic aromatic hydrocarbon present in diesel particulates, is a mutagen in Salmonella typhimurium and a tumorigen in laboratory animals. The activation of 1-nitropyrene to a bacterial mutagen has been attributed to nitroreduction; however, the metabolic pathways involved in its metabolism to a tumorigen are not known, but may involve nitroreduction, ring oxidation, or a combination of the two. In these experiments, we examined the importance of ring oxidation in the activation of 1-nitropyrene (99.85 to 99.98 percent 1-nitropyrene, 0.15 to 0.02 percent 1,3-, 1,6-, and 1,8-dinitropyrene by mass spectral analyses) to a mammalian-cell mutagen and carcinogen. Chinese hamster ovary cells were used to assess the mutagenicity of ring-oxidized 1-nitropyrene metabolites. In the absence of a rat liver 9,000 x g supernatant, 6-hydroxy-1-nitropyrene, 1-nitropyrene-9,10-oxide, and pyrene-4,5-oxide were the most mutagenic compounds tested. 3-Hydroxy-1-nitropyrene, 8-hydroxy-1-nitropyrene, and 1-nitropyrene-4,5-oxide were weaker mutagens, whereas pyrene and 1-nitropyrene were essentially nonmutagenic. The order of mutagenic potency with S9 was: 1-nitropyrene-4,5-oxide greater than 6-hydroxy-1-nitropyrene approximately 1-nitropyrene-9,10-oxide greater than 1-nitropyrene approximately 3-hydroxy-1-nitropyrene approximately 8-hydroxy-1-nitropyrene greater than pyrene approximately pyrene-4,5-oxide, with the last two compounds being nearly nonmutagenic. The epoxide hydrase inhibitor 1,2-epoxy-3,3,3-trichloropropane increased the mutation frequency fivefold. In addition, guinea pig liver microsomes and Aroclor-induced rat liver microsomes, which increased the formation of 1-nitropyrene-4,5-oxide and 1-nitropyrene-9,10-oxide, increased the mutagenic response. Incubation of 1-nitropyrene-4,5-oxide with calf thymus DNA resulted in the formation of three DNA adducts. A similar adduct pattern was observed when Chinese hamster ovary cells were incubated with the oxide. Inclusion of a nitroreductase, xanthine oxidase, in the in vitro incubations resulted in the formation of an additional adduct identified as N-(deoxyguanosin-8-yl)-1-aminopyrene. This adduct was not observed in Chinese hamster ovary cells treated with 1-nitropyrene-4,5-oxide. 1-Nitropyrene-9,10-oxide reacted with calf thymus DNA to give an adduct pattern similar to that observed with 1-nitropyrene-4,5-oxide. The distribution of adducts was not affected by conducting the reactions in the presence of xanthine oxidase.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Role of ring oxidation in the metabolic activation of 1-nitropyrene. 177 57

Two versions of the 32P-postlabeling assay (nuclease P1 and butanol extraction) enhance the detection limit of polycyclic aromatic hydrocarbon (PAH)-modified DNA. Previously published studies suggest that DNA adducts derived from N-substituted aryl compounds are poorly recovered in the nuclease P1 version. In this study, both versions were employed to ascertain whether the apparent differences in sensitivity could be used to select diagnostically for nitroaromatic-DNA adducts derived by treating calf thymus DNA with organic extracts isolated from four diesel and one gasoline vehicle emission particles. We enhanced the formation of nitrated-PAH-derived adducts through xanthine oxidase (XO)-catalyzed nitroreduction of nitrated-PAHs, constituents previously detected in the diesel emissions. Chromatographic mobilities of the XO-derived DNA adducts were compared to adducts detected in calf thymus DNA resulting from rat liver S9-mediated metabolism. All four diesel organic extracts treated with XO resulted in the formation of one major DNA adduct, chromatographically distinct from the multiple DNA adducts detected in the rat liver S9-treated incubations. This adduct was detectable with the butanol extraction but not the nuclease P1 version of the 32P-postlabeling assay and was chromatographically similar to DNA adducts formed following XO nitroreduction of 1-nitropyrene or ascorbic acid treatment of 1-nitro-8-nitroso-pyrene and 1-nitro-6-nitrosopyrene. In contrast, when S9 activation was used, multiple DNA adducts were detected along a diagonal zone of radioactivity and were radioactively labeled with equivalent efficiency irrespective of the assay version employed. The in vitro calf thymus DNA model described in this study enhances the diagnostic potential of the 32P-postlabeling assay through the selective formation of nuclease P1-sensitive N-substituted aryl-derived DNA adducts.
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PMID:Improvement in the diagnostic potential of 32P-postlabeling analysis demonstrated by the selective formation and comparative analysis of nitrated-PAH-derived adducts arising from diesel particle extracts. 189 29

The 32P-postlabeling technique was used to qualitatively establish the pattern of DNA adduct formation in mammary tissue and liver following administration of 1-nitropyrene to female Sprague-Dawley rats. 1-Nitropyrene (100 mg/kg b.w.) was administered by gavage in trioctanoin and the rats were sacrificed 24 h later. DNA was isolated from mammary fat pads and liver, enzymatically hydrolyzed to deoxyribonucleoside-3'-monophosphates and then converted to [5'-32P]3',5'-bisphosphates. The polyethyleneimine-cellulose (PEI-cellulose) TLC 32P-fingerprints revealed the presence of multiple putative adducts in the mammary fat pads and in the livers. To investigate the role of nitroreduction in the formation of these adducts, calf thymus DNA was incubated with [3H]1-nitropyrene in vitro in the presence of xanthine oxidase. The DNA was isolated and analyzed by the 32P-postlabeling technique. A major adduct spot was detected and confirmed as N-(deoxyguanosin-8-yl)-1-aminopyrene. This adduct cochromatographed with a minor in vivo adduct of DNA obtained from mammary fat pads and livers. However, the major adducts detected in vivo did not appear to originate from simple nitroreduction of 1-nitropyrene. The results of this study suggest that other metabolic pathways, such as ring oxidation, or ring oxidation followed by nitroreduction, may be responsible for the putative 1-nitropyrene-DNA adducts observed in mammary fat pads and livers of female Sprague-Dawley rats.
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PMID:32P-postlabeling analysis of 1-nitropyrene-DNA adducts in female Sprague-Dawley rats. 291 May 23

The antitumor antibiotic mitomycin C is shown to form a covalent complex with calf thymus DNA under anaerobic conditions in the presence of either NADPH cytochrome c reductase/NADPH, xanthine oxidase/NADH, or the chemical reducing system H2/PtO2. Digestion of the complex with DNase I/snake venom diesterase/alkaline phosphatase yields a single mitomycin deoxyguanosine adduct as the major DNA alkylation product, identified as N2-(2'' beta,7''-diaminomitosen-1'' alpha-yl) 2'-deoxyguanosine (Structure 2). Two minor adducts, 2-5% each of the total adduct pool, are isolated and identified as the 1'' beta stereoisomer of 2 (Structure 3), and 10''-decarbamoyl-2 (Structure 7). The same results were obtained with M13 DNA and poly(dG-dC).poly(dG-dC); however, in the latter case, a minor adduct apparently possessing two deoxyguanosine and one mitomycin unit is isolated. Digestion of the covalent mitomycin-calf thymus DNA complex with nuclease P1 yields four dinucleotide adducts, all of which consist of 2 linked at its 3' end to each of the four possible 5' nucleotides (A, T, G, and C). Upon treatment of each dinucleotide adduct with snake venom diesterase/alkaline phosphatase, 2 is released along with the corresponding free nucleoside. In apparent conflict with the present results, previous reports from another laboratory have indicated that modification of calf thymus DNA by mitomycin C under conditions identical to those described here result in the isolation of three mitomycin C mononucleotide adducts possessing linkages of the drug to N2 and O6 of guanine and N6 of adenine. Evidence is shown suggesting that the latter adducts are actually three of the above four dinucleotide derivatives of 2 obtained independently by us and, thus, all of them in fact possess an identical N2-mitosenylguanine adduct moiety. Model-building studies indicate an excellent fit of the guanine N2-linked drug molecule inside the minor groove of B-DNA with no appreciable distortion of the DNA structure.
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PMID:Reaction of DNA with chemically or enzymatically activated mitomycin C: isolation and structure of the major covalent adduct. 301 44

1-Nitropyrene, 1-nitrosopyrene and 1-aminopyrene were investigated for their ability to induce covalently bound DNA adducts in calf thymus DNA and Chinese hamster lung fibroblasts. Xanthine oxidase catalysed the induction of one major and one minor DNA adduct in 1-nitropyrene- or 1-nitrosopyrene-treated calf thymus DNA, whilst 1-aminopyrene was inactive. These compounds did not form detectable DNA adducts in the absence of xanthine oxidase. The major DNA adduct produced by 1-nitropyrene and 1-nitrosopyrene in calf thymus DNA co-migrated on h.p.l.c., and the structure was consistent with that previously described by others as N-(deoxyguanosin-8-yl)-1-aminopyrene. The compounds were investigated for their ability to form DNA adducts in Chinese hamster lung fibroblasts. 1-Nitropyrene (5.2 pmol/mg DNA/h) and 1-nitrosopyrene (129 pmol/mg DNA/h) formed a single DNA adduct in Chinese hamster lung cells which co-eluted on h.p.l.c. with the C-8 deoxyguanosine adduct isolated from 1-nitropyrene-treated calf thymus DNA. 1-Nitrosopyrene was the most efficient compound investigated for the production of the C-8 guanine adducts. In contrast, 1-aminopyrene (14.7 pmol/mg DNA/h) induced the formation of a DNA adduct which did not co-elute with the C-8 guanine adduct. The data presented here suggest that 1-nitropyrene and 1-aminopyrene are metabolized to reactive intermediates which form different DNA adducts in Chinese hamster lung fibroblasts.
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PMID:The induction of DNA adducts in mammalian cells exposed to 1-nitropyrene and its nitro-reduced derivatives. 333 73

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