Showing papers on "Demethylase published in 1981"

p-Chloro-N-methylaniline demethylase activity in liver and extrahepatic tissues of the human fetus and in chick embryo liver.

Abstract: We achieved a 50-fold increase in sensitivity of a fluorescence assay for p-chloro-N-methylaniline (p-CNMA) demethylase enabling us to examine the kinetics of the reaction in chick embryo liver and human fetal tissues and its inducibility in chick embryo liver. In chick embryo liver, p-CNMA demethylase activity was maximally induced (to about 200% of control levels) by both phenobarbital and beta-naphthoflavone. p-CNMA demethylase is therefore nonselective in its response to inducers of the P-450 and P-448 classes, respectively. Line-weaver-Burk plots of the data suggest that single kinetic components predominated in the reaction for both control and induced livers (mean apparent KmS: control, 3.8 X 10(-5) M; phenobarbital treated, 3.8 X 10(-5) M). Differences in the KmS and the pH-activity curves for the phenobarbital- and beta-naphthoflavone-induced enzymes suggested, however, that the induced enzymes were not identical. p-CNMA demethylase activity was measurable in liver and extrahepatic organs of the human fetus and was 1.5 times higher in human fetal liver than in chick embryo liver. At least two kinetic components participated in the reaction in the human liver. Reaction rates in human fetal adrenal, lung and brain were about 60, 2 and 1% of the liver rates, respectively. Detection of mixed function oxidase activity in human fetal brain, not usually considered a site of biotransformation, suggests that the fetal brain could be a site of cytotoxic activation of chemicals during human fetal development.

Studies on the incubation mixtures for the in vitro mutagenesis test with metabolic activation (microsomal assay) = 2. Behaviour of cytochromes P-450, P-420, b5, of NADPH-CYT. C-reductases, and p-nitroanisole demethylase.

Abstract: Cytochromes P-450, P-420, b5, NADPH-cytochrome c-reductase, aminopyrine and p-nitroanisole demethylase and lipid peroxidation were determined at various times in the incubation mixtures for the in vitro microsomal assay for the mutagenic activity of xenobiotics. No effect was observed on cytochromes b5 and P-420. A decrease in cytochrome P-450 (about 50% in 2 hrs.) and a much faster decrease of aminopyrine demethylase and NADPH cytochrome c-reductase (about 50% in 30 min) was noted with mice microsomes. With S9 liver fraction of rat, p-nitroanisole demethylase activity was much more stable than aminopyrine demethylase activity in the presence of lipid peroxidation, but the decrease was faster and at comparable rates for both activities in the presence of 50 mM styrene. The use of simple colorimetric assay as proves of microsomal monooxygenase activity and the importance of this kind of enzyme studies for a better understanding of the in vitro mutagenesis results are discussed.