Tryptophan catabolism in Bacillus megaterium

Abstract

Bacillus megaterium grows in a medium containing L-tryptophan as the sole carbon, nitrogen, and energy source. Kynurenine, anthranilic acid, and catechol are metabolic intermediates, suggesting that this organism used the anthranilic acid pathway for tryptophan degradation. Cells that grow on L-tryptophan oxidize kynurenine, alanine, and anthranilic acid and the presence of tryptophan oxygenase (EC 1.13.1.12), kynureninase (EC 3.7.1.3), and catechol oxygenase (EC 1.13.1.1) in cell extracts provide additional evidence for the degradative pathway in B. megaterium. Tryptophan oxygenase is inhibited by sodium azide, potassium cyanide, and hydroxylamine, indicating that the enzyme has a functional heme group. D-Tryptophan is not a substrate for tryptophan oxygenase, and the D-isomer does not inhibit this enzyme. Formamidase (EC 3.5.1.9) and anthranilate hydroxylase are not detectable in extracts. Tryptophan catabolism is inducible in B megaterium and is subject to catabolite repression by glucose and glutamate. Arginine does not cause repression, and kynurenine induces both tryptophan oxygenase and kynureninase.