NADPH-generating system: influence on microsomal mono-oxygenase stability during incubation for the liver-microsomal assay with rat and mouse S9 fractions.
Activity levels of 7-ethoxycoumarin O-deethylase (ED), aminopyrine N-demethylase (APD), p-nitroanisole O-demethylase (p-NAD) and glucose-6-phosphate dehydrogenase (G-6-PDH) were determined in incubation mixtures for the liver-microsomal assay (LMA) at time 0 and after 1 and 2 h incubation under conditions for mutagenic assay. The experiments were performed with S9 liver fractions from mice (induced with Na-phenobarbital and beta-naphthoflavone) and rats (induced with Aroclor 1254) with and without G-6-PDH in the incubation mixtures. In the absence of G-6-PDH the activities were significantly lower at time 0 in the mouse. The pattern of stability, however, was similar for the activities, with an increase of stability after 1 and 2 h of pre-incubation (an exception for p-NAD). Only ED activity showed a similar behaviour in the rat. No differences were present for APD and p-NAD activities at time 0 in the rat, but the enzyme stabilities were significantly decreased after 2 h of incubation (about 15% and 10% for APD and p-NAD respectively) in the absence of G-6-PDH. At time 0, the amounts of G-6-PDH differed between mouse and rat fractions; however, during the incubations for LMA they decreased by about 57% and 53% for the two species, respectively. In addition to the above biochemical results, the presence of exogenous G-6-PDH in the incubations for the mutagenic assay, significantly increased the mitotic gene conversion and mitotic crossing-over of dimethylnitrosamine (DMN) and AR2MNFN (a nitroimidazo[2,1-b]thiazole) in the D7 strain of Saccharomyces cerevisiae.
D015660:7-Alkoxycoumarin O-Dealkylase; D000633:Aminopyrine N-Demethylase / Q000378:metabolism; D000818:Animals; D001711:Biotransformation; D003434:Crossing Over, Genetic / Q000187:drug effects; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000494:pharmacology*; D009154:Mutation; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010090:Oxidoreductases, O-Demethylating / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics
D009153:Mutagens; D009249:NADP; C026048:4-nitroanisole O-demethylase; D006899:Mixed Function Oxygenases; D010090:Oxidoreductases, O-Demethylating; D005954:Glucosephosphate Dehydrogenase; D010105:Oxygenases; D015660:7-Alkoxycoumarin O-Dealkylase; D000633:Aminopyrine N-Demethylase