MetaCyc Reaction:

Superclasses: Reactions Classified By Conversion TypeSimple ReactionsChemical Reactions
Reactions Classified By SubstrateSmall-Molecule Reactions

EC Number:,

Enzymes and Genes:

Brevibacillus brevis S1: tryptophan dioxygenaseInferred from experiment
Cupriavidus metallidurans CH34: tryptophan dioxygenaseInferred from experiment: kynA
Delftia acidovorans: tryptophan dioxygenaseInferred from experiment
Homo sapiens: indoleamine 2,3-dioxygenaseInferred from experiment: INDO
tryptophan 2,3-dioxygenaseInferred from experiment: TDO2
Saccharomyces cerevisiae: tryptophan 2,3-dioxygenaseInferred by computational analysis: BNA2
Streptomyces anulatus: tryptophan 2,3-dioxygenaseInferred from experiment: acmG
Streptomyces parvulus: tryptophan dioxygenaseInferred from experiment

In Pathway: L-tryptophan degradation XI (mammalian, via kynurenine), L-tryptophan degradation I (via anthranilate), L-tryptophan degradation to 2-amino-3-carboxymuconate semialdehyde, 3-hydroxy-4-methyl-anthranilate biosynthesis

Supersedes EC numbers:,

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.

Mass balance status: Balanced.

Enzyme Commission Primary Name for tryptophan 2,3-dioxygenase

Enzyme Commission Synonyms for tryptophan pyrrolase (ambiguous), tryptophanase, tryptophan oxygenase, tryptamine 2,3-dioxygenase, tryptophan peroxidase, indoleamine 2,3-dioxygenase (ambiguous), indolamine 2,3-dioxygenase (ambiguous), L-tryptophan pyrrolase, TDO, L-tryptophan 2,3-dioxygenase

Enzyme Commission Primary Name for indoleamine 2,3-dioxygenase

Enzyme Commission Synonyms for IDO (ambiguous), tryptophan pyrrolase (ambiguous)

Standard Gibbs Free Energy (ΔrG in kcal/mol): -89.69Inferred by computational analysis [Latendresse13]

Enzyme Commission Summary for
A protohemoprotein. In mammals, the enzyme appears to be located only in the liver. This enzyme, together with EC, indoleamine 2,3-dioxygenase, catalyses the first and rate-limiting step in the kynurenine pathway, the major pathway of tryptophan metabolism [Littlejohn03]. The enzyme is specific for tryptophan as substrate, but is far more active with L-tryptophan than with D-tryptophan [Ren96].

Enzyme Commission Summary for
A protohemoprotein. Requires ascorbic acid and methylene blue for activity. This enzyme has broader substrate specificity than EC, tryptophan 2,3-dioxygenase [Yamamoto67]. It is induced in response to pathological conditions and host-defense mechanisms and its distribution in mammals is not confined to the liver [Yasui86]. 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 [Yasui86, Littlejohn03]. Superoxide radicals can replace O2 as oxygen donor [Hirata77, Thomas99].

Citations: [Dang00, Leeds93, Uchida83, Takikawa86, Sono90 ]

Gene-Reaction Schematic

Gene-Reaction Schematic

Unification Links: KEGG:R00678, KEGG:R00678, Rhea:24536

Relationship Links: BRENDA:EC:, BRENDA:EC:, ENZYME:EC:, ENZYME:EC:, IUBMB-ExplorEnz:EC:, IUBMB-ExplorEnz:EC:, UniProt:RELATED-TO:P21643

Revised 13-Sep-2012 by Caspi R, SRI International


Dang00: Dang Y, Dale WE, Brown OR (2000). "Comparative effects of oxygen on indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase of the kynurenine pathway." Free Radic Biol Med 28(4);615-24. PMID: 10719243

Hirata77: Hirata F, Ohnishi T, Hayaishi O (1977). "Indoleamine 2,3-dioxygenase. Characterization and properties of enzyme. O2- complex." J Biol Chem 252(13);4637-42. PMID: 194886

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Leeds93: Leeds JM, Brown PJ, McGeehan GM, Brown FK, Wiseman JS (1993). "Isotope effects and alternative substrate reactivities for tryptophan 2,3-dioxygenase." J Biol Chem 268(24);17781-6. PMID: 8349662

Littlejohn03: Littlejohn TK, Takikawa O, Truscott RJ, Walker MJ (2003). "Asp274 and his346 are essential for heme binding and catalytic function of human indoleamine 2,3-dioxygenase." J Biol Chem 278(32);29525-31. PMID: 12766158

Ren96: Ren S, Liu H, Licad E, Correia MA (1996). "Expression of rat liver tryptophan 2,3-dioxygenase in Escherichia coli: structural and functional characterization of the purified enzyme." Arch Biochem Biophys 333(1);96-102. PMID: 8806758

Sono90: Sono M (1990). "Spectroscopic and equilibrium studies of ligand and organic substrate binding to indolamine 2,3-dioxygenase." Biochemistry 29(6);1451-60. PMID: 2334706

Takikawa86: Takikawa O, Yoshida R, Kido R, Hayaishi O (1986). "Tryptophan degradation in mice initiated by indoleamine 2,3-dioxygenase." J Biol Chem 261(8);3648-53. PMID: 2419335

Thomas99: Thomas SR, Stocker R (1999). "Redox reactions related to indoleamine 2,3-dioxygenase and tryptophan metabolism along the kynurenine pathway." Redox Rep 4(5);199-220. PMID: 10731095

Uchida83: Uchida K, Shimizu T, Makino R, Sakaguchi K, Iizuka T, Ishimura Y, Nozawa T, Hatano M (1983). "Magnetic and natural circular dichroism of L-tryptophan 2,3-dioxygenases and indoleamine 2,3-dioxygenase. I. Spectra of ferric and ferrous high spin forms." J Biol Chem 258(4);2519-25. PMID: 6600455

Yamamoto67: Yamamoto S, Hayaishi O (1967). "Tryptophan pyrrolase of rabbit intestine. D- and L-tryptophan-cleaving enzyme or enzymes." J Biol Chem 242(22);5260-6. PMID: 6065097

Yasui86: Yasui H, Takai K, Yoshida R, Hayaishi O (1986). "Interferon enhances tryptophan metabolism by inducing pulmonary indoleamine 2,3-dioxygenase: its possible occurrence in cancer patients." Proc Natl Acad Sci U S A 83(17);6622-6. PMID: 2428037

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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