Kynureninase and Kynurenine 3-Hydroxylase in Mammalian Tissues
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The major pathway of tryptophan catabolism in mammals is the kynurenine pathway. L-Tryptophan 2,3-dioxygenase, which is localized in liver and is induced by loading of tryptophan or treatment with glucocorticoids, initiates this pathway. Other organs, however, contain indoleamine 2,3-dioxygenase which is a different enzyme protein from tryptophan 2,3-dioxygenase but yields the same product, formylkynurenine, from tryptophan. Under normal conditions, formylkynurenine is mainly produced by liver tryptophan 2,3-dioxygenase. Kynurenine produced by formamidase is either hydroxylated to 3-hydroxykynurenine, hydrolytically cleaved to form anthranilic acid and alanine, or transaminated to produce kynurenic acid (Scheme 1).
KeywordsAnthranilic Acid Kynurenic Acid Kynurenine Pathway Organ Distribution Tryptophan Metabolism
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