Tryptophan 5-hydro, Xenopus/Amphibian,ylase 1 (TPH) catalyzes the following reaction: L-tryptophan + tetrahydrobiopterin + O2 = 5-hydro, Xenopus/Amphibian,y-L-tryptophan + 4a-hydro, Xenopus/Amphibian,ytetrahydrobiopterin. TPH belongs to the biopterin-dependent aromatic amino acid hydro, Xenopus/Amphibian,ylase family. The activity of TPH is enhanced by phosphorylation by cAMP-dependent protein kinase (PKA) and Ca2+/calmodulin kinase II (CaM K II). CaM K II phosphorylates Ser19 which lies within the regulatory domain of TPH2.