FIGURE 1.

Overview of host tryptophan metabolism via serotonin synthesis and degradation pathway. The key metabolites and enzymes during tryptophan metabolism are presented. AADC, aromatic L-amino acid decarboxylase; AANAT, aralkylamine N-acetyltransfer; ASMT, acetylserotonin O-methyltransferase; IDO, indoleamine 2,3-dioxygenase; KMO, kynurenine 3-monooxygenase; KYN, kynurenine; KYNA, kynurenic acid; NAD, nicotinamide adenine dinucleotides; NAS, N-acetyl-serotonin; QUIN, quinolinic acid; TDO, tryptophan 2,3-dioxygenase; Tph1/2, tryptophan hydroxylase 1/2; 3HANA, 3-hydroxyanthranilic acid; 3-HK, 3-hydroxykynurenine; 5-HTP, 5-hydroxytryptophan.