Kynurenine—oxoglutarate transaminase

Thus, the two substrates of this enzyme are L-kynurenine and 2-oxoglutarate, whereas its two products are 4-(2-aminophenyl)-2,4-dioxobutanoate and L-glutamate. The former product is an unstable α-oxo acid that quickly undergoes intramolecular cyclization to form kynurenic acid.

This enzyme belongs to the family of transferases, to be specific, the transaminases, that transfer nitrogenous groups. The systematic name of this enzyme class is L-kynurenine:2-oxoglutarate aminotransferase. Other names in common use include kynurenine transaminase (cyclizing), kynurenine 2-oxoglutarate transaminase, kynurenine aminotransferase, and L-kynurenine aminotransferase. This enzyme participates in tryptophan metabolism. It employs one cofactor, pyridoxal phosphate.

KYAT1, AADAT (aka KYAT2), and KYAT3 are examples of enzymes of this class. GOT2 (aka KYAT4) is also believed to catalyze the above reaction.

Structural studies

As of early 2009, 18 structures have been solved for this class of enzymes, with PDB accession codes 1X0M, 1YIY, 1YIZ, 1W7L, 1W7M, 1W7N, 3E2F, 3E2Y, 3E2Z, 2ZJG, 2YGZ, 2Z61, 2R5C, 2R2N, 2R5E, 3B46, 3DC1, and 2QLN.

References

Han Q, Cai T, Tagle DA, Robinson H, Li J (August 2008). "Substrate specificity and structure of human aminoadipate aminotransferase/kynurenine aminotransferase II". Bioscience Reports. 28 (4): 205–15. doi:10.1042/BSR20080085. PMC 2559858. PMID 18620547.
Guidetti P, Amori L, Sapko MT, Okuno E, Schwarcz R (July 2007). "Mitochondrial aspartate aminotransferase: a third kynurenate-producing enzyme in the mammalian brain". Journal of Neurochemistry. 102 (1): 103–11. doi:10.1111/j.1471-4159.2007.04556.x. PMID 17442055. S2CID 20413002.

Bonner DM, Jakoby WB (August 1956). "Kynurenine transaminase from neurospora". The Journal of Biological Chemistry. 221 (2): 689–95. doi:10.1016/S0021-9258(18)65181-6. PMID 13357462.
Mason M (July 1957). "Kynurenine transaminase of rat kidney; a study of coenzyme dissociation". The Journal of Biological Chemistry. 227 (1): 61–8. doi:10.1016/S0021-9258(18)70795-3. PMID 13449053.
Rossi F, Han Q, Li J, Li J, Rizzi M (November 2004). "Crystal structure of human kynurenine aminotransferase I". The Journal of Biological Chemistry. 279 (48): 50214–20. doi:10.1074/jbc.M409291200. PMID 15364907.
Chon H, Matsumura H, Koga Y, Takano K, Kanaya S (November 2005). "Crystal structure of a human kynurenine aminotransferase II homologue from Pyrococcus horikoshii OT3 at 2.20 A resolution". Proteins. 61 (3): 685–8. doi:10.1002/prot.20614. PMID 16138312. S2CID 35477005.
Han Q, Gao YG, Robinson H, Ding H, Wilson S, Li J (May 2005). "Crystal structures of Aedes aegypti kynurenine aminotransferase". The FEBS Journal. 272 (9): 2198–206. doi:10.1111/j.1742-4658.2005.04643.x. PMID 15853804. S2CID 38329597.
Han Q, Robinson H, Cai T, Tagle DA, Li J (February 2009). "Biochemical and structural properties of mouse kynurenine aminotransferase III". Molecular and Cellular Biology. 29 (3): 784–93. doi:10.1128/MCB.01272-08. PMC 2630683. PMID 19029248.
Han Q, Robinson H, Li J (February 2008). "Crystal structure of human kynurenine aminotransferase II". The Journal of Biological Chemistry. 283 (6): 3567–73. doi:10.1074/jbc.M708358200. PMID 18056995.
Rossi F, Garavaglia S, Montalbano V, Walsh MA, Rizzi M (February 2008). "Crystal structure of human kynurenine aminotransferase II, a drug target for the treatment of schizophrenia". The Journal of Biological Chemistry. 283 (6): 3559–66. doi:10.1074/jbc.M707925200. PMID 18056996.
Han Q, Cai T, Tagle DA, Robinson H, Li J (August 2008). "Substrate specificity and structure of human aminoadipate aminotransferase/kynurenine aminotransferase II". Bioscience Reports. 28 (4): 205–15. doi:10.1042/BSR20080085. PMC 2559858. PMID 18620547.
Han Q, Gao YG, Robinson H, Li J (February 2008). "Structural insight into the mechanism of substrate specificity of aedes kynurenine aminotransferase". Biochemistry. 47 (6): 1622–30. doi:10.1021/bi701800j. PMC 2858008. PMID 18186649.
Wogulis M, Chew ER, Donohoue PD, Wilson DK (February 2008). "Identification of formyl kynurenine formamidase and kynurenine aminotransferase from Saccharomyces cerevisiae using crystallographic, bioinformatic and biochemical evidence". Biochemistry. 47 (6): 1608–21. doi:10.1021/bi701172v. PMID 18205391.

v t e Transferase: nitrogenous groups (EC 2.6)
2.6.1: Transaminases	Aspartate transaminase GOT1 GOT2 Alanine transaminase GABA transaminase Tyrosine aminotransferase Kynurenine—oxoglutarate transaminase Ornithine aminotransferase Branched-chain amino acid aminotransferase Alanine—glyoxylate transaminase AGXT
2.6.3: Oximinotransferases	Oximinotransferase
2.6.99: Other	Pyridoxine 5'-phosphate synthase

v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)

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