EC - Indoleamine 2,3-dioxygenase

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IntEnz Enzyme Nomenclature


Accepted name:
indoleamine 2,3-dioxygenase
Other names:
IDO [ambiguous]
tryptophan pyrrolase [ambiguous]
D-tryptophan:oxygen 2,3-oxidoreductase (decyclizing)
Systematic name:
D-tryptophan:oxygen 2,3-oxidoreductase (ring-opening)




A protohemoprotein. Requires ascorbic acid and methylene blue for activity. This enzyme has broader substrate specificity than EC, tryptophan 2,3-dioxygenase [1]. It is induced in response to pathological conditions and host-defense mechanisms and its distribution in mammals is not confined to the liver [2]. While the enzyme is more active with D-tryptophan than L-tryptophan, its only known function to date is in the metabolism of L-tryptophan [2,6]. Superoxide radicals can replace O2 as oxygen donor [4,7].

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00684
Structural data: CSA , EC2PDB
Gene Ontology: GO:0033754


  1. Yamamoto, S. and Hayaishi, O.
    Tryptophan pyrrolase of rabbit intestine. D- and L-tryptophan-cleaving enzyme or enzymes.
    J. Biol. Chem. 242: 5260-5266 (1967). [PMID: 6065097]
  2. Yasui, H., Takai, K., Yoshida, R. and Hayaishi, O.
    Interferon enhances tryptophan metabolism by inducing pulmonary indoleamine 2,3-dioxygenase: its possible occurrence in cancer patients.
    Proc. Natl. Acad. Sci. USA 83: 6622-6626 (1986). [PMID: 2428037]
  3. Takikawa, O., Yoshida, R., Kido, R. and Hayaishi, O.
    Tryptophan degradation in mice initiated by indoleamine 2,3-dioxygenase.
    J. Biol. Chem. 261: 3648-3653 (1986). [PMID: 2419335]
  4. Hirata, F., Ohnishi, T. and Hayaishi, O.
    Indoleamine 2,3-dioxygenase. Characterization and properties of enzyme •O2- complex.
    J. Biol. Chem. 252: 4637-4642 (1977). [PMID: 194886]
  5. Dang, Y., Dale, W.E. and Brown, O.R.
    Comparative effects of oxygen on indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase of the kynurenine pathway.
    Free Radic. Biol. Med. 28: 615-624 (2000). [PMID: 10719243]
  6. Littlejohn, T.K., Takikawa, O., Truscott, R.J. and Walker, M.J.
    Asp274 and His346 are essential for heme binding and catalytic function of human indoleamine 2,3-dioxygenase.
    J. Biol. Chem. 278: 29525-29531 (2003). [PMID: 12766158]
  7. Thomas, S.R. and Stocker, R.
    Redox reactions related to indoleamine 2,3-dioxygenase and tryptophan metabolism along the kynurenine pathway.
    Redox Rep. 4: 199-220 (1999). [PMID: 10731095]
  8. Sono, M.
    Spectroscopic and equilibrium studies of ligand and organic substrate binding to indolamine 2,3-dioxygenase.
    Biochemistry 29: 1451-1460 (1990). [PMID: 2334706]

[EC created 2006]