Tryptophan decarboxylase pyrrolase

Fig. 244. Degradation of L-tryptophan via kynurenine and 3-hydroxyanthranilic acid 1 Tryptophan 2,3-dioxygenase (tryptophan pyrrolase, C 2.5) 2 formamidase 3 kynurenine 3-monooxygenase 4 kynureninase 5 3-hydroxyanthranilate 3,4-dioxygenase 6 aminocarhoxy-muconate semialdehyde decarboxylase 7 aminomuconate semialdehyde dehydrogenase 8 0x0-glutarate dehydrogenase system 9 spontaneous cyclization...

A third pathway of protocatechuic acid metabolism occurs in a Rhodo-pseudomonas. Proctor and Scher (1960) have reported that this organism forms protocatechuate from benzoate, then decarboxylates the product to catechol. (This is the second example of a nonoxidative aromatic decarboxylase.) Subsequent metabolism of catechol yields a keto acid not yet identified, but possibly that produced in other catechol-utilizing systems described below. A unique feature of the Rhodopseudomonas system is its reported dependence on hydrogen peroxide for the oxidation of catechol. It will be of interest to learn whether peroxide is consumed stoichiometrically in the reaction, or whether it is an activator, as has been found for tryptophan pyrrolase. 

The metabolism of tryptophan has been of interest to investigators in many different fields of biochemistry and medicine. The biological transformations of this indole derivative are very complex and involve a series of enzymes, which cause i) changes of the side chain (transaminases, decarboxylases, etc.) ii) splitting of the indole nucleus from the side chain (tryptophanase) iii) changes in the pyrrole nucleus (tryptophan pyrrolase, kynureninase, etc.) iiii) changes in the benzene ring (hydroxylases, etc.). 

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