[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Argininosuccinate lyase (ASL)

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

# Argininosuccinate lyase (ASL)

Argininosuccinate lyase splits argininosuccinate into arginine and fumarate; the fumarate links the urea cycle to the Krebs cycle.

Updated 2026-11-01

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## Key facts

- Argininosuccinate → arginine + fumarate; an elimination that spends no energy.
- Fumarate goes to malate and oxaloacetate, which gives aspartate again: the «Krebs bicycle».
- It is a tetramer from the same family as fumarase.
- It also helps deliver arginine to nitric oxide synthase.

**EC number**
[4.3.2.1](https://www.enzyme-database.org/query.php?ec=4.3.2.1)

**Genes**
ASL

**Structure (PDB)**
[1K62](https://www.rcsb.org/structure/1K62)

## Structure

- 1K62 is human ASL carrying the Q286R variant, with no substrate bound.

## Regulation

- No important allosteric control is known; protein-rich diet and glucocorticoids induce it.

## Inhibitors and toxins

- No inhibitors are used clinically.

## Clinical notes

- Argininosuccinic aciduria: hyperammonaemia, trichorrhexis nodosa (brittle hair), hepatomegaly and arterial hypertension from less nitric oxide.
- High argininosuccinate in plasma and urine confirms the diagnosis.

## Pathways

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

## Related conditions

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

## Related

- [Argininosuccinate synthetase (ASS)](https://durgical.com/en/biochemistry/enzymes/argininosuccinate-synthetase/)
- [Arginase 1](https://durgical.com/en/biochemistry/enzymes/arginase-1/)
- [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/)

## Test yourself

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

## Which two products does argininosuccinate lyase release?

Arginine, which stays in the urea cycle, and fumarate, which enters the Krebs cycle.

## Which hair sign suggests argininosuccinic aciduria?

Trichorrhexis nodosa: brittle hair with nodes that break.

## What is the «Krebs bicycle»?

The link between the two cycles: urea cycle fumarate goes back to oxaloacetate and aspartate, which re-enters the urea cycle.

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

Sources: [ASL: Argininosuccinate lyase (human)](https://www.uniprot.org/uniprotkb/P04424/entry) (UniProt, 2026); [Argininosuccinic aciduria: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/argininosuccinic-aciduria/) (MedlinePlus, US National Library of Medicine, 2026); [1K62: Crystal Structure of the Human Argininosuccinate Lyase Q286R Mutant](https://www.rcsb.org/structure/1K62) (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/argininosuccinate-lyase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/argininosuccinate-lyase/