Synergistic and product induction of the enzymes of tryptophan metabolism in Pseudomonas acidovorans

Abstract

The process of induction of tryptophan oxygenase in Pseudomonas acidovorans is typical of many microbial enzyme induction systems, in that it (i) requires cell multiplication and de novo protein synthesis, (ii) is subject to catabolite repression, (iii) results in the formation of a stable enzyme, whose level, upon removal of inducer, is diluted out by cell proliferation, and (iv) exhibits product induction. l-Kynurenine was more effective than l-tryptophan as an inducer of both tryptophan oxygenase and the second enzyme of the pathway, kynurenine formamidase. The occurrence of product induction of these two enzymes by their common metabolite eliminated the possibility of sequential induction of these enzymes. dl-5-Fluorotryptophan, nonmetabolizable and devoid of any inducing activity, resulted in a concentration-dependent inhibition of the l-tryptophan-mediated induction of tryptophan oxygenase; kynurenine formamidase induction, however, was not influenced by the presence of dl-5-fluorotryptophan. dl-7-Azatryptophan, also nonmetabolizable and completely inactive as an inducer, acted synergistically with l-tryptophan and superinduced tryptophan oxygenase levels. When induction was conducted in a medium containing only l-tryptophan and 7-azatryptophan as inducing agents, then tryptophan oxygenase induction was enhanced, whereas the kynurenine formamidase level was essentially unchanged. These data indicate that various inducing conditions affect the relative proportions of tryptophan oxygenase and kynurenine formamidase, and thus indicate noncoordinate regulation of these enzyme activities.