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. 2023 Jun 21;10:1209613. doi: 10.3389/fnut.2023.1209613

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Endogenous pathways of tryptophan metabolism including Kynurenine Pathway (left) and 5-Hydroxyindole Pathway (right). IDO, indoleamine 2,3-dioxygenase; TDO, tryptophan 2,3-dioxygenase; KMO, kynurenine 3-monooxygenase; KAT, kynurenine aminotransferase; 3-HAO, 3-hydroxyanthranilicacid 3,4-dioxygenase; ACMSD, 2-amino-3-carboxymuconate-6-semialdehydedecarboxylase; QPRT, quinolinate phosphoribosyltransferase; and NAD⁺, nicotinamide adenine dinucleotides⁺.