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[Biochemistry](https://durgical.com/en/biochemistry/) · Enzyme

# Arginase 1

Arginase 1 closes the urea cycle in the liver cytosol: it releases urea and regenerates ornithine.

Updated 2026-11-01

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## Key facts

- Arginine + H₂O → urea + ornithine; the only step that makes urea.
- A metalloenzyme with two Mn²⁺ ions that activate the water molecule.
- Arginase 2 (mitochondrial, mainly kidney) has no part in the urea cycle.
- It competes with nitric oxide synthase for arginine.

**EC number**
[3.5.3.1](https://www.enzyme-database.org/query.php?ec=3.5.3.1)

**Genes**
ARG1

**Structure (PDB)**
[2AEB](https://www.rcsb.org/structure/2AEB)

## Structure

- 2AEB: human arginase 1 at 1.29 Å with the inhibitor ABH, which mimics the transition state and binds both manganese ions.

## Regulation

- Glucocorticoids, glucagon and protein-rich diets induce it.

## Inhibitors and toxins

- ABH and nor-NOHA (experimental)
- Ornithine and lysine (weak)

## Clinical notes

- Arginase deficiency: progressive spastic diplegia, seizures and developmental delay; hyperammonaemia is usually mild.
- In some tumours, arginase-expressing myeloid cells use up arginine and switch off T cells.

## Pathways

- [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/)

## Related conditions

- [Hyperammonaemia](https://durgical.com/en/conditions/hyperammonaemia/)

## Related

- [Argininosuccinate lyase (ASL)](https://durgical.com/en/biochemistry/enzymes/argininosuccinate-lyase/)
- [Urea](https://durgical.com/en/biochemistry/molecules/urea/)
- [Ornithine transcarbamylase (OTC)](https://durgical.com/en/biochemistry/enzymes/ornithine-transcarbamylase/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which metal does arginase 1 need?

Two manganese ions (Mn²⁺) that activate water to hydrolyse arginine.

## How does arginase deficiency differ from the other cycle defects?

Progressive spastic diplegia dominates and ammonia usually rises only a little.

## Which molecule does arginase regenerate for the next turn?

Ornithine, which returns to the mitochondrion to take up another carbamoyl phosphate.

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

Sources: [ARG1: Arginase-1 (human)](https://www.uniprot.org/uniprotkb/P05089/entry) (UniProt, 2026); [Arginase deficiency: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/arginase-deficiency/) (MedlinePlus, US National Library of Medicine, 2026); [2AEB: Crystal structure of human arginase I at 1.29 A resolution and exploration of inhibition in immune response.](https://www.rcsb.org/structure/2AEB) (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/arginase-1/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/arginase-1/