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.
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
Related conditions
Related
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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: ASL: Argininosuccinate lyase (human) (UniProt, 2026); Argininosuccinic aciduria: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 1K62: Crystal Structure of the Human Argininosuccinate Lyase Q286R Mutant (RCSB Protein Data Bank, 2026).
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