Induction by l -Tryptophan and an Analogue, α-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, α-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 α-methyl- dl -tryptophan caused the accumulation of endogenous tryptophan, and that induction by the nonmetabolizable analogue is induction by the endogenous tryptophan.