Precursor to metabolite: 5-hydroxytryptophan to Serotonin

5-hydroxytryptophan is converted to Serotonin by AADC.

The pair

5-hydroxytryptophan — Serotonin precursor (5-HTP); OTC supplement, no receptor action of its own.
Serotonin — The endogenous ligand at fourteen receptor subtypes; the home of serotonicity — synaptic serotonin elevation.