ABSTRACT
N-Methylation may be among the more important reactions by which amino groups are modified, although this functional group is well endowed with several other means for its oxidation and conjugation (Jakoby et al., 1982). Conjugation as a route of metabolism also allows acetylation (Chapter 6); glycosylation, particularly by N-glucuronidation (Chapter 4); N-sulfation to form sulfamates (Chapter 5); and, possibly, carbamylation (Elvin et al., 1980). Recognition of Nmethylation, among the first of the conjugation reactions that was observed, occurred when His (1887) examined the urine of dogs after administration of pyridine and thereby discovered its conversion to the N-methylpyridinium ion. A large group of animals produced the same metabolic product (Abderhalden and Brahm, 1909; Totani and Hoshioi, 1910), and the reaction was subsequently extended to a broader group of substrates (Williams, 1947). First recognized in lung (Brown et al., 1959a, 1959b), enzymes that catalyze methylation at nitrogen have been found in extracts of liver, skin, brain and kidney, among other tissues.
