Studies on the metabolism of tryptophan in ATCC 15926 revealed different metabolic routes for the L-and D-isomer besides the biosynthetic pathway for pyrrolnitrin synthesis. L-Tryptophan catabolism follows the aromatic route via anthranilic acid. Tryptophan 2,3-dioxygenase was induced by L-tryptophan. Kynureninase and anthranilate 1,2-dioxygenase were induced by L-tryptophan, L-kynurenine and anthranilic acid. Anthranilate 1,2-dioxygenase was absent from a mutant strain of ATCC 15926 which produced about 30-fold increased amounts of pyrrolnitrin. The values of tryptophan 2,3-dioxygenase and kynureninase did not differ substantially between the two strains. Kynurenine 3-monooxygenase, 3-hydroxyanthranilate 3,4-dioxygenase, tryptophanase and indolyl-3-alkane α-hydroxylase activities were not detected. D- and L-tryptophan were converted to indole-3-pyruvate by tryptophan amino-transferase and via indole-3-acetaldehyde to indole-3-acetic acid. This additional catabolic pathway as well as tryptophan racemase activity was constitutive and present in both strains.


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