PMID: 6401221Feb 1, 1983Paper

High-affinity nitrosamine dealkylase system in rat liver microsomes and its induction by fasting

Cancer Research
Y Y Tu, C S Yang

Abstract

In order to elucidate the enzymic basis of nitrosamine metabolism, the in vitro metabolism of nitrosamines by rat liver microsomes and the effects of fasting on the microsomal enzymes have been studied. Fasting for 1 to 3 days causes a 2- to 3-fold enhancement of the reduced nicotinamide adenine dinucleotide phosphate-dependent nitrosodimethylamine demethylase (NDMAD) activity. The cytochrome P-450 content and the activities of reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase and benzphetamine demethylase, however, are only modestly increased. Gel electrophoretic analysis reveals the induction of a 50,000-dalton protein band during fasting. The induction of this protein band as well as the enhancement of NDMAD activity are inhibited by CoCl2 and inhibitors of protein and RNA biosynthesis. The involvement of cytochrome P-450 in the NDMAD is supported by the fact that microsomal reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase is required for the demethylase activity. Kinetic analysis indicates that a low-Km form of NDMAD (apparent Km, 0.07 mM) is markedly induced by fasting. With microsomes of control rats, there are at least three apparent Km values (0.07, 0.38, and 38...Continue Reading

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