title: Stability of microsomal mono-oxygenase during incubations for the liver microsomal assay with S9 fractions of mouse liver under various inductions.
abstract: Aminopyrine-N-demethylase and p-nitroanisole-O-demethylase activities were determined in incubation mixtures for the liver microsomal assay at time zero and after 1 h of incubation in the conditions for the mutagenic assay. The experiments were performed with the S9 liver fraction of mice in the basal state and induced with sodium phenobarbital, beta-naphthoflavone or both. Lipid peroxidation was also determined. The experiments were repeated with female mice and also in the presence of styrene, as an example of a xenobiotic substance. The activity of pNAD was much more stable than that of APD in all the conditions tested. The pattern of stability, however, was similar for the two activities: more stable than controls with S9 fractions from beta-NF-induced mice, less stable than controls in PB-induced mice, intermediate between controls and PB-induced mice in those with combined induction by PB + beta NF. Styrene 50 mM in the incubation mixtures led to a marked inactivation of enzymic activity, similar in all cases and reaching about 90% in 1 h. S9 fractions from female mice gave enzymes slightly more stable in almost all cases. Lipid peroxidation was appreciably more elevated in basal than in induced animals. It was concluded that, for a mutagenesis test on an unknown xenobiotic, S9 fractions from mice following PB and beta-NF induction are to be preferred from the point of view of activation.
mesh_terms: D000633:Aminopyrine N-Demethylase / Q000378:metabolism*; D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D005260:Female; D008054:Lipid Peroxides / Q000378:metabolism; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009152:Mutagenicity Tests / Q000379:methods; D009575:Nitroanisole O-Demethylase / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D020058:Styrene; D013343:Styrenes / Q000494:pharmacology; D019324:beta-Naphthoflavone
chemical_list: D001571:Benzoflavones; D008054:Lipid Peroxides; D013343:Styrenes; D020058:Styrene; D019324:beta-Naphthoflavone; D009575:Nitroanisole O-Demethylase; D010088:Oxidoreductases; D000633:Aminopyrine N-Demethylase; D010634:Phenobarbital