Biochemistry · Enzyme
Tyrosine hydroxylase !
Tyrosine hydroxylase makes L-DOPA from tyrosine: the rate-limiting step for making dopamine, noradrenaline and adrenaline.
Updated 2026-11-01
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Key facts
- Tyrosine + BH4 + O₂ → L-DOPA + dihydrobiopterin + H₂O; it needs Fe²⁺.
- It is the rate-limiting step of catecholamine synthesis.
- It is found in dopaminergic and noradrenergic neurons and in the adrenal medulla.
- Dopamine and noradrenaline slow it by feedback.
Structure
- 6ZN2: human tyrosine hydroxylase with dopamine bound to the active-site iron (cryo-electron microscopy, 4.3 Å).
Regulation
- Catecholamines inhibit it by binding the iron.
- Phosphorylation of its regulatory domain (PKA and other kinases) activates it and releases bound dopamine.
Inhibitors and toxins
- Metirosine (α-methyl-p-tyrosine)
Clinical notes
- Metirosine lowers catecholamine synthesis in phaeochromocytoma.
- Tyrosine hydroxylase deficiency causes a childhood dystonia that may respond to L-DOPA.
- In Parkinson disease the substantia nigra neurons that express it are lost.
Pathways
Related conditions
Related
Test yourself
Think of the answer, then tap the question to see it.
What is the rate-limiting step of catecholamine synthesis?
Tyrosine hydroxylase, which turns tyrosine into L-DOPA.
Which drug inhibits it, and in which tumour is it used?
Metirosine, to cut catecholamine production in phaeochromocytoma.
How do its own products slow it down?
Dopamine and noradrenaline bind the active-site iron; phosphorylation of the regulatory domain releases them.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: TH: Tyrosine 3-monooxygenase (human) (UniProt, 2026); TH gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 6ZN2: Partial structure of tyrosine hydroxylase in complex with dopamine showing the catalytic domain and an alpha-helix from the regulatory domain involved in dopamine binding. (RCSB Protein Data Bank, 2026).
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