Catecholamines

Route: Tyrosine → L-DOPA (3,4-dihydroxyphenylalanine) → Dopamine → Norepinephrine → Epinephrine

Tyrosine hydroxylase adds a hydroxyl group to the ring of tyrosine and gives L-DOPA. It has an iron atom in the active site and uses oxygen and tetrahydrobiopterin (BH₄), like phenylalanine hydroxylase. Reviews call it the rate-limiting enzyme of catecholamine synthesis. The oxidized BH₄ is regenerated by pterin-4a-carbinolamine dehydratase and dihydropteridine reductase. Aromatic L-amino acid decarboxylase, a pyridoxal phosphate enzyme, removes the carboxyl group of L-DOPA and gives dopamine. Dopamine beta-hydroxylase adds a hydroxyl group to the carbon next to the ring and gives norepinephrine. It has two copper ions per subunit and takes electrons from ascorbate (vitamin C). In humans it sits in secretory vesicles, as a soluble protein in the lumen and bound to the vesicle membrane. The last enzyme, phenylethanolamine N-methyltransferase, transfers a methyl group from S-adenosylmethionine to the amino group of norepinephrine and gives epinephrine. Dopamine and norepinephrine are neurotransmitters, and epinephrine regulates fuel use. Together the three are called catecholamines and act as stress-signal molecules in the fight-or-flight response.

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Steps

Molecules

Build any of these from its atoms.

• Tyrosine Build it
• L-DOPA (3,4-dihydroxyphenylalanine) Build it
• Dopamine Build it
• Norepinephrine Build it
• Epinephrine 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).