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B6db references: 96064386

type Journal Article
authors Kataoka, K.; Kinouchi, T.; Akimoto, S.; Ohnishi, Y.
title Bioactivation of cysteine conjugates of 1-nitropyrene oxides by cysteine conjugate beta-lyase purified from Peptostreptococcus magnus
journal Appl Environ Microbiol
ui 96064386
year (1995)
volume 61
number 11
pages 3781-7.
keywords Animal
abstract 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)
last changed 2002/11/12 16:17

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