Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
 ...
PMID:Role of intestinal microflora in metabolism of glutathione conjugates of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide. 130 95

To determine the role of cysteine conjugate beta-lyase (beta-lyase) in the metabolism of mutagenic nitropolycyclic aromatic hydrocarbons, we determined the effect of beta-lyase on the mutagenicities and DNA binding of cysteine conjugates of 4,5-epoxy-4,5-dihydro-1-nitropyrene (1-NP 4,5-oxide) and 9,10-epoxy-9,10-dihydro-1-nitropyrene (1-NP 9,10-oxide), which are detoxified metabolites of the mutagenic compound 1-nitropyrene. We purified beta-lyase from Peptostreptococcus magnus GAI0663, since P. magnus is one of the constituents of the intestinal microflora and exhibits high levels of degrading activity with cysteine conjugates of 1-nitropyrene oxides (1-NP oxide-Cys). The activity of purified beta-lyase was optimal at pH 7.5 to 8.0, was completely inhibited by aminooxyacetic acid and hydroxylamine, and was eliminated by heating the enzyme at 55 degrees C for 5 min. The molecular weight of beta-lyase was 150,000, as determined by fast protein liquid chromatography. S-Arylcysteine conjugates were good substrates for this enzyme. As determined by the Salmonella mutagenicity test, 5 ng of beta-lyase protein increased the mutagenicity of the cysteine conjugate of 1-NP 9,10-oxide (10 nmol per plate) 4.5-fold in Salmonella typhimurium TA98 and 4.1-fold in strain TA100. However, beta-lyase had little effect on the cysteine conjugate of 1-NP 4,5-oxide (10 nmol per plate). Both conjugates exhibited only low levels of mutagenicity with nitroreductase-deficient strain TA98NR. In vitro binding of 1-NP oxide-Cys to calf thymus DNA was increased by adding purified beta-lyase or xanthine oxidase.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Bioactivation of cysteine conjugates of 1-nitropyrene oxides by cysteine conjugate beta-lyase purified from Peptostreptococcus magnus. 852 86