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[Biochemistry](https://durgical.com/en/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.

**EC number**
[1.14.16.2](https://www.enzyme-database.org/query.php?ec=1.14.16.2)

**Genes**
TH

**Structure (PDB)**
[6ZN2](https://www.rcsb.org/structure/6ZN2)

## 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

- [Catecholamine synthesis and breakdown](https://durgical.com/en/biochemistry/pathways/catecholamine-synthesis-and-breakdown/)

## Related conditions

- [Phaeochromocytoma](https://durgical.com/en/conditions/phaeochromocytoma/)
- [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/)

## Related

- [Tyrosine](https://durgical.com/en/biochemistry/molecules/tyrosine/)
- [Tetrahydrobiopterin (BH4)](https://durgical.com/en/biochemistry/molecules/tetrahydrobiopterin/)
- [Phenylalanine hydroxylase (PAH)](https://durgical.com/en/biochemistry/enzymes/phenylalanine-hydroxylase/)
- [Molecules derived from amino acids](https://durgical.com/en/biochemistry/topics/molecules-derived-from-amino-acids/)

## 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.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [TH: Tyrosine 3-monooxygenase (human)](https://www.uniprot.org/uniprotkb/P07101/entry) (UniProt, 2026); [TH gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/th/) (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.](https://www.rcsb.org/structure/6ZN2) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/tyrosine-hydroxylase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/tyrosine-hydroxylase/