FIGURE 1.

Schematic representation of tryptophan metabolism pathways leading to production of neuro-active compounds. The pathways correspond to metabolism of tryptophan (indicated in green font inside an oval) for production of six neuro-active compounds namely, indole, tryptamine, kynurenine, quinolinate, indole acetic acid, and indole propionic acid. These six compounds have been indicated in green font. The intermediate compounds of the pathways have been represented in black font. For each pathway, the EC numbers and the functional domains of the participating enzymes have been indicated in blue and red colors, respectively.