Bioactivation of cysteine conjugates of 1-nitropyrene oxides by cysteine conjugate beta-lyase purified from Peptostreptococcus magnus.
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)
Department of Bacteriology, School of Medicine, University of Tokushima, Japan.
K
K
Kataoka
T
T
Kinouchi
S
S
Akimoto
Y
Y
Ohnishi
D000818:Animals; D001711:Biotransformation; D013437:Carbon-Sulfur Lyases; D002417:Cattle; D003545:Cysteine / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D066298:In Vitro Techniques; D008190:Lyases / Q000302:isolation & purification / Q000378:metabolism*; D009153:Mutagens / Q000378:metabolism / Q000493:pharmacokinetics; D010084:Oxidation-Reduction; D010462:Peptostreptococcus / Q000201:enzymology*; D011721:Pyrenes / Q000378:metabolism* / Q000493:pharmacokinetics; D013379:Substrate Specificity
D009153:Mutagens; D011721:Pyrenes; D004247:DNA; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase; D003545:Cysteine; C032668:1-nitropyrene