Tryptophan and the biosynthesis of nicotinamide

Abstract

Nicotinamide was formed by washed and broken Escherichia coli and by their undialyzed and dialyzed washings, but not by exhaustively washed cell fragments, in salt solns. containing sources of N other than tryptophan, such as ammonium ions or orithine; the formation was increased by the addition of tryptophan. No nicotinamide was formed by these cell prepns. in the presence of tryptophan when no other source of N was present. The effect of rising doses of tryptophan on the nicotinamide synthesis by washed E. coli reached a max. at concns. of 1-2 m[image]; a further increase of the concn. did not increase the synthesis of nicotinamide. In rats comparative expts. on the effect of tryptophan administered either orally or intraperit. confirmed the importance of the intestinal flora for the action of tryptophan on the nicotinamide metabolism. By feeding rising doses of tryptophan it was shown that as in E. coli, a saturation point could be reached. The bearings of these findings on the possible role of tryptophan in the biosynthesis of nicotinamide were discussed. It could best be explained by a kind of catalytic action of tryptophan on the nicotinamide synthesis.