Catalyzes the hydroxylation of L-kynurenine (L-Kyn) to form 3-hydroxy-L-kynurenine (L-3OHKyn) (PubMed:23575632, PubMed:26752518, PubMed:28604669, PubMed:29208702, PubMed:29429898). Required for synthesis of quinolinic acid, a neurotoxic NMDA receptor antagonist and potential endogenous inhibitor of NMDA receptor signaling in axonal targeting, synaptogenesis and apoptosis during brain development. Quinolinic acid may also affect NMDA receptor signaling in pancreatic beta cells, osteoblasts, myocardial cells, and the gastrointestinal tract (Probable). {ECO:0000269|PubMed:23575632, ECO:0000269|PubMed:26752518, ECO:0000269|PubMed:28604669, ECO:0000269|PubMed:29208702, ECO:0000269|PubMed:29429898, ECO:0000305|PubMed:12402501}. This is the function of ENSG00000117009 (KMO, kynurenine 3-monooxygenase).