IDO2 (indolamine-2,3-dioxygenase) is an enzyme with protein size of 420 amino acids (47 kDa) that is used for catabolism of tryptophan. In organisms, other enzymes participate in L-tryptophan cleavage, namely IDO1 and TDO. Despite of IDO1 and IDO2 are closely related enzymes originating by gene duplication and sharing high level (43%) of sequence homology,[6][7] they differentiate by their kinetics, function and expression pattern. Genes encoding IDO1 and IDO2 have similar genomic structure and are situated closely to each other on chromosome 8.[8] IDO2 is produced in a very limited type of tissues as kidney, liver or antigen presenting cells.[9] IDO2 is less active on substrates of IDO1, better catabolizing other Trp derivates as 5-methoxytryptophan. There are several isoforms in population that comes from alternative splicing.[10] As well as IDO1, IDO2 has been reported in Treg differentiation in vitro,[11] suggesting a role in tolerance maintenance. Its expression has been found in several cancers, gastric, colon or renal tumors.[12]
^Löb S, Königsrainer A, Zieker D, Brücher BL, Rammensee HG, Opelz G, Terness P (January 2009). "IDO1 and IDO2 are expressed in human tumors: levo- but not dextro-1-methyl tryptophan inhibits tryptophan catabolism". Cancer Immunology, Immunotherapy. 58 (1): 153–7. doi:10.1007/s00262-008-0513-6. PMID18418598. S2CID6199515.
Meininger D, Zalameda L, Liu Y, Stepan LP, Borges L, McCarter JD, Sutherland CL (December 2011). "Purification and kinetic characterization of human indoleamine 2,3-dioxygenases 1 and 2 (IDO1 and IDO2) and discovery of selective IDO1 inhibitors". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics. 1814 (12): 1947–54. doi:10.1016/j.bbapap.2011.07.023. PMID21835273.
