The nicotinamide-saving action of tryptophan and the biosynthesis of nicotinamide by the intestinal flora of the rat

Abstract

Admn. of tryptophan causes an increase of urinary nicotinamide methochloride elimination in adult rats kept on a mixed diet. This increase is markedly greater after oral than after parenteral admn. The increase in urinary nicotinamide methochloride output caused by tryptophan admn. is markedly reduced in rats in which feeding of succinylsulfathiazole has produced a reduction in basal nicotinamide methochloride elimination, but not by sulfathiazole. Ornithine, proline and delta-aminovaleric acid do not cause an increase of nicotinamide methochloride output in the rat. Ornithine, and to a lesser extent arginine and gluta-mine, increase the formation of nicotinamide by Escherichia coli. Methionine and choline, which are inactive by themselves, increase the nicotinamide formation from ornithine by E. coli, while hexamethylenetetramine is ineffective in this respect. The conversion of ornithine into nicotinamide by E. coli seems not to depend on maintaining intact the structure of the bacterial cell. E. coli in pure culture does not convert tryptophan into nicotina-mide, but mixed cultures from the content of the rat''s cecum perform this conversion. The compound formed by bacterial synthesis is nicotinamide and not nicotinic acid. The conversion of tryptophan into nicotinamide in the rat is discussed. It is suggested that the intestinal flora plays an important role in this process and that ornithine is an intermediate in this conversion.