Tryptophan peroxidase-oxidase system

Hydroxytryptophan was not metabolized by a tryptophan-adapted strain of Pseudomonas (217) and was not attacked by the tryptophan peroxidase-oxidase system (217, 884). The enteramine and kynurenine pathways are quite distinct, as is supported by the facts that synthetic 5-hydroxykynurenine (124, 574), the expected product of tryptophan peroxidase-oxidase action, does not act as an ommochrome precursor in insects or as a nicotinic acid precursor in Neurospora (124). 

Tryptophan is, however, not the only agent which can bring about an increase in tryptophan peroxidase-oxidase. A smaller effect can be produced by substances which initiate the stress reaction of the adrenal-pituitary system (478). High X-irradiation produces a similar effect in normal, but not in adrenalectomized, animals (869). Cortisone reverses the effect of adrenalectomy (868), and glucocorticoids (e.g., cortisone and hydrocortisone) can themselves cause an increase in the enzyme (484). How these changes are brought about is still obscure their elucidation... 

When synthesis of this compound was accomplished, > experiments with it made it clear that it is not a normal tryptophan metabolite. The metabolism of oxindolylalanine was found to be quite different from that of tryptophan or kynurenine in rat liver slices, or in the intact animal. The paper chromatographs of the urines from normal and pyridoxine-deficient rats fed oxindolylalanine were quite different from those obtained when tryptophan was fed. Furthermore, the tryptophan peroxidase-oxidase enzyme system does not act on this compound, nor was it metabolized by the bacillus. Pseudomonas fluorescens, which had been adapted to tryptophan or kynurenine. The identity of the first intermediate of tryptophan oxidation, therefore, is still unknown. 

The first well-defined step in tryptophan catabolism is the splitting of the indole ring with the formation of formylkynurenine. This is accomplished by a labile enzyme system present only in liver which is composed of a tryptophan peroxidase and an oxidase which produces hydrogen peroxide as a product of its activity. This coupled oxidation system induces the reaction given in the following equation ... 

There is another type of oxidative process which might be classified among the energizing reactions. The first step in the oxidation of tryptophan to formyl kynurenine is catalyzed by a peroxidase-H202 system.Aerobic oxidases such as xanthine oxidase, d-amino acid oxidase, and urico-oxidase produce H2O2 during oxidation of their respective... 

Two enzyme systems have been discovered that initiate the catabolism of tryptophan and lead to the products shown in Fig. 13. These are tryptophan oxidase-peroxidase and kynureninase. Their roles in the catabolic process will be discussed below. 

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