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.
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
Related conditions
Related
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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: ARG1: Arginase-1 (human) (UniProt, 2026); Arginase deficiency: MedlinePlus Genetics (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. (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.