Catabolite Repression of Tryptophanase in Escherichia coli

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RESUMO

Catabolite repression of tryptophanase was studied in detail under various conditions in several strains of Escherichia coli and was compared with catabolite repression of β-glactosidase. Induction of tryptophanase and β-galactosidase in cultures grown with various carbon sources including succinate, glycerol, pyruvate, glucose, gluconate, and arabinose is affected differently by the various carbon sources. The extent of induction does not seem to be related to the growth rate of the culture permitted by the carbon source during the course of the experiment. In cultures grown with glycerol as carbon source, preinduced for β-galactosidase or tryptophanase and made permeable by ethylenediaminetetraacetic acid (EDTA) treatment, catabolite repression of tryptophanase was not affected markedly by the addition of cAMP (3′,5′-cyclic adenosine monophosphate). Catabolite repression by glucose was only partially relieved by the addition of cAMP. In contrast, under the same conditions, cAMP completely relieved catabolite repression of β-galactosidase by either pyruvate or glucose. Under conditions of limited oxygen, induction of tryptophanase is sensitive to catabolite repression; under the same conditions, β-galactosidase induction is not sensitive to catabolite repression. Induction of tryptophanase in cells grown with succinate as carbon source is sensitive to catabolite repression by glycerol and pyruvate as well as by glucose. Studies with a glycerol kinaseless mutant indicate that glycerol must be metabolized before it can cause catabolite repression. The EDTA treatment used to make the cells permeable to cAMP was found to affect subsequent growth and induction of either β-galactosidase or tryptophanase much more adversely in E. coli strain BB than in E. coli strain K-12. Inducation of tryptophanase was reduced by the EDTA treatment significantly more than induction of β-galactosidase in both strains. Addition of 2.5 × 10−3m cAMP appeared partially to reverse the inhibitory effect of the EDTA treatment on enzyme induction but did not restore normal growth.

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