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.

Amidohydrolases↗

PubMed1969

Product induction in Pseudomonas acidovorans of a permease system which transports L-tryptophan.

Growth of Pseudomonas acidovorans in the presence of l-tryptophan resulted in the appearance of a tryptophan transport system which was extremely sensitive to sodium azide or 2,4-dinitrophenol. Asparagine-grown cells possessed no detectable tryptophan "permease" activity. Substitution of l-kynurenine for l-tryptophan in the growth medium also induced the tryptophan permease activity, along with tryptophan oxygenase and kynurenine formamidase. This is the first reported example of the product induction of a permease activity. Irrespective of whether Pseudomonas cells are grown in the presence of d- or l-tryptophan, the resulting induced tryptophan permease activity is specific for the l-isomer. In addition, the radioactive compounds l-leucine, l-phenylalanine, or dl-5-hydroxytryptophan are not transported. When dl-5-fluorotryptophan is a component of the inducing medium (with l-tryptophan), induction of tryptophan permease activity, as well as tryptophan oxygenase, is inhibited. In the permease assay system, using normally induced cells, the fluoroanalogue inhibited strikingly tryptophan transport. Therefore, this analogue may inhibit induction by blocking inducer transport into the cell. When added to the l-tryptophan-inducing medium, dl-7-azatryptophan markedly enhanced induction of tryptophan oxygenase, but the level of tryptophan permease activity was not further elevated. The mechanism of this analogue is unclear at present. Invariant tryptophan permease activity levels are found in cells grown with 5 or 15 mml-tryptophan or 5 mml-kynurenine, whereas the respective tryptophan oxygenase levels are greatly different. Together with other results, these results indicate that the synthesis of tryptophan permease activity is not coordinate with that of tryptophan oxygenase. Tryptophan transport is strongly inhibited by l-formylkynurenine and by l-kynurenine. These two metabolites were prepared in radioactive form, and they are actively transported following bacterial growth on l-tryptophan or l-kynurenine. Preliminary results suggest the tryptophan permease activity may be distinct from the permease(s) activity for l-formylkynurenine and l-kynurenine. Kynurenine, then, is capable of inducing tryptophan permease and kynurenine permease activities.

Asparagine↗

PubMed1968