Kynureninase and Kynurenine 3-Hydroxylase in Mammalian Tissues

  • E. Okuno
  • R. Kido
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 294)


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).


Anthranilic Acid Kynurenic Acid Kynurenine Pathway Organ Distribution Tryptophan Metabolism 
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Copyright information

© Plenum Press, New York 1991

Authors and Affiliations

  • E. Okuno
    • 1
  • R. Kido
    • 1
  1. 1.Department of BiochemistryWakayama Medical CollegeWakayama 640Japan

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