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The effects of ethanol on the metabolism of nitrosamines by rat liver microsomes have been studied. Treatment of rats with 10 or 15% ethanol in drinking water for 3 days causes a 4- to 5-fold enhancement in microsomal N-nitrosodimethylamine demethylase (NDMAd) activity and a 40-60% increase in gross P-450 content. The enhancement is mainly due to the induction of a low Km form (Km = 0.07 mM) of NDMAd. The treatment induces protein species with molecular weights between 50000 and 52000, some of which are believed to be P-450 isozymes with high affinity to NDMA. In addition to NDMA, treatment with ethanol also enhances the metabolism of N-nitroso-N-methylethylamine, N-nitrosomethylaniline, and N-nitroso-N-methylbenzylamine. When added to the incubation mixture, ethanol and its homologs inhibit the demethylation of these nitrosamines by microsomes. Ethanol is a competitive inhibitor of the low Km NDMAd with a Ki of 0.31 mM and is less effective in inhibiting the metabolism of more lipophilic nitrosamines.

The nature of the denitrosation of nitrosamines by rat liver microsomes was investigated. The rates of NADPH-dependent nitrosamine demethylation and denitrosation were compared in the same incubation mixture using several types of microsomes and inhibitors. Pretreatment with isopropanol, pyrazole, phenobarbital, and 3-methylcholanthrene had parallel effects on the microsomal demethylation and denitrosation reactions. Nitrite was produced with N-nitrosodimethylamine, N-nitroso-N-methylethylamine, N-nitroso-N-methylbutylamine, N-nitroso-methylbenzylamine, or N-nitroso-N-methylaniline as a substrate. With control microsomes, the rate of the denitrosation reaction was 9-39% that of demethylation depending on the type and concentration of nitrosamines used. Using nitrosodimethylamine as the substrate, the Km of denitrosation was about twice that of the demethylation reaction. Several polar organic solvents such as ethanol and isopropanol inhibited the denitrosation and demethylation reactions and each solvent inhibited both reactions to about the same extent. In the presence of cumene hydroperoxide, microsomes can catalyze the denitrosation of nitrosodimethylaime which is also accompanied by demethylation. Studies with a reconstituted system and with inhibitors indicate that the denitrosation reaction requires the presence of both cytochrome P-450 and NADPH-cytochrome-P-450 reductase. The results suggest that the denitrosation is closely linked to the demethylation reaction.

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Carcinoembryonic antigen (CEA) was purified from GW-39 human tumor xenografts in hamsters by immunoaffinity chromatography. Binding of the antigen to immobilized monoclonal antibody provided a high degree of purification of CEA in a single step. A recovery of 79% and a 750-fold purification were obtained. The purified CEA has a molecular size of 180 kilodaltons, an isoelectric point of 4.4, and a specific activity of 0.94. About 73% of the radiolabeled GW-39 CEA reacted with goat anti-CEA serum. The amino acid and carbohydrate compositions of the GW-39 CEA were comparable to those of CEA preparations from other sources.