Serotonin

Route: Tryptophan → 5-Hydroxytryptophan → Serotonin (5-hydroxytryptamine)

Tryptophan hydroxylase adds a hydroxyl group at position 5 of the indole ring of tryptophan and gives 5-hydroxytryptophan. Like tyrosine hydroxylase it has an iron atom in the active site and uses oxygen and tetrahydrobiopterin (BH₄), and reviews call it the rate-limiting enzyme of serotonin synthesis. The BH₄ is regenerated as in the tyrosine hydroxylase step. Humans have two forms, TPH1 and TPH2, and TPH2 works in neurons. The structure shown is TPH1. Aromatic L-amino acid decarboxylase, a pyridoxal phosphate enzyme, removes the carboxyl group and gives serotonin (5-hydroxytryptamine). It is the same enzyme that makes dopamine from L-DOPA. Serotonin regulates mood. It is also found in the gastrointestinal tract, where it regulates intestinal contraction, and in platelets, where it facilitates vasoconstriction.

Practice this pathway All pathways

Steps

Molecules

Build any of these from its atoms.

• Tryptophan Build it
• 5-Hydroxytryptophan Build it
• Serotonin (5-hydroxytryptamine) Build it

Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).