Catabolism (from Greek κάτω kato, "downward" and βάλλειν ballein, "to throw") is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy or used in other anabolic reactions.
In biochemistry, the addition of a formyl functional group is termed formylation.
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO) is a heme-containing enzyme that in humans is encoded by the IDO1 gene.
L-Kynurenine is a metabolite of the amino acid L-tryptophan used in the production of niacin.
Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins.