Kynureninase and Kynurenine 3-Hydroxylase in Mammalian Tissues
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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- Braunshtein, A.E., Goryachenkova, E.V., and Paskhina, T.S., 1949, Enzymlc formation of alanine from L-kynurenine and L-tryptophan and the role of vitamin B6 in this process, Biokhimiya, 14: 163–179.Google Scholar
- Ishikawa, T., Okuno, E., Kawai, E., Kawai, J., and Kido, R., 1989, Organ distribution, purification and characterization of kynureninase in Suncus Murinus (Insectivore) and anthranilic acid level in the serum, Comp. Biochem. Physiol., 93B: 107–111.Google Scholar
- Nishimoto, Y., Takeuchi, F., and Shibata, Y., 1975, Isolation of L-kynurenine 3-hydroxylase from the mitochondrial outer membrane of rat liver, J. Biochem., 78: 573–581.Google Scholar