Kynureninaseisapyridoxal-5-phosphatedependentenzymethatcatalyzesthehydrolyticcleavageoftheaminoacidsL-kynurenineandL-3-hydroxykynureninetogiveeitheranthranilicacidor3-hydroxyanthranilicacidandalanine(1).Theenzymeisamemberofthe“kynureninepathway”enzymes,throughwhichthemajorityofdietarytryptophanisdegradedintheliver,andisinvolvedinthedenovobiosynthesisofNAD+(2,3).Kynureninepathwaygenesareexpressedinimmunesystemcellssuchasmacrophagesandmicroglia.Duringinflammatoryresponses,thekynureninepathwayinthesecellsproducesquinolinicacid(QA)andnotNAD+.QAexcitesneuronsviatheactivationofNMDA(NmethylDaspartate)receptorsresultinginneuronaldamage.ThetissuedamagingprocesshasbeendemonstratedinAIDrelateddementiacomplex,Alzheimer’s,stroke,epilepsy,andHuntington’sdisease.BecauseKynureninaseisoneofthekeyenzymesofQAproduction,itsinhibitorsmaybeusefulforthetreatmentofneurologicaldisorders.TherecombinantKynureninasehasbeenshowntopossessspecificityfor3-hydroxykynurenineoverkynurenine(4,5).

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