title: Isotope effects in enzymatic N-demethylation of tertiary amines.
abstract: The N-demethylation of 1-(N-methyl-N-trideuteriomethylamino)-3-phenylpropane (1) by rodent liver homogenates was studied. The ratio of 1-trideuteriomethylamino-3-phenylpropane (2)/1-methylamino-3-phenylpropane (3) was determined by gc-ms. The ratio of 2/3 in the product of N-demethylation of 1 by liver homogenate from phenobarbital-treated rats was 1.31 and from untreated rats was 1.32, and the differences between the two groups were not statistically significant. The ratio of 2/3 in the product obtained from N-demethylation of 1 by liver homogenates from mice was 1.45. The ratio of 2/3 of greater than unity indicates the presence of a kinetic primary isotopes effect in the enzymatic N-demethylation reaction. This effect is exclusive of the secondary isotope effects on the amino nitrogen. The presence of this primary isotope effect indicates that the cleavage of the C-H bond of the N-methyl group is a rate-limiting step in the N-demethylation of tertiary amines by rodent microsomal enzymes.
mesh_terms: D000588:Amines / Q000378:metabolism*; D000818:Animals; D003640:Dealkylation; D003903:Deuterium; D007536:Isomerism; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D000588:Amines; D003903:Deuterium; D010089:Oxidoreductases, N-Demethylating; D010634:Phenobarbital