Induction by L-tryptophan and an analogue, alpha-methyl-DL-tryptophan, of the enzymes catabolizing L-tryptophan in Pseudomonas

Abstract

An investigation was made of the pattern of induction of the enzymes that metabolize l-tryptophan through kynurenic acid (the quinoline pathway) in Pseudomonas fluorescens. The first four enzymes in the pathway were not induced in the same proportions or in the same time courses. This lack of coordinate induction excludes a mechanism of regulation of these enzymes at a single site as proposed in the operon model. The enzymes were induced in a sequential pattern in the order of their position on the pathway, when they became the limiting reactions. The nonmetabolizable analogue, alpha-methyl-dl-tryptophan, caused a measurable elevation in the levels of the first three enzymes of the same pathway. Evidence is presented that growth of the cells in the presence of alpha-methyl-dl-tryptophan caused the accumulation of endogenous tryptophan, and that induction by the nonmetabolizable analogue is induction by the endogenous tryptophan.