| Property | Summary |
|---|---|
| Gene name | **ASL** (argininosuccinate lyase; argininosuccinase) in **Homo sapiens** (human) (pqac-00000003, pqac-00000034) |
| UniProt accession | **P04424** |
| Chromosome location | **Chromosome 7**; reported as **7q11.21 / cen-q11.2**, with gene structure including exon 0 for 5' UTR and 16 coding exons (pqac-00000003, pqac-00000034, pqac-00000036) |
| Protein size | **464 aa**, about **52 kDa per monomer** (tetramer ~208 kDa) (pqac-00000006, pqac-00000009) |
| Quaternary structure | **Homotetramer** with **4 active sites**; each active site is formed at the interface of **three subunits** (pqac-00000002, pqac-00000003, pqac-00000006) |
| EC number | **EC 4.3.2.1** (argininosuccinate lyase) (pqac-00000008) |
| Reaction catalyzed | Reversible cleavage of **argininosuccinate → L-arginine + fumarate**; this is the 4th step of the urea cycle and also supplies arginine in the citrulline-NO cycle (pqac-00000000, pqac-00000003, pqac-00000013) |
| Substrate specificity | Physiologic substrate is **argininosuccinic acid (argininosuccinate)**; ASL is the only enzyme capable of generating endogenous arginine in mammalian cells (pqac-00000006, pqac-00000018) |
| Catalytic mechanism | **β-elimination (ElcB)** mechanism with a **carbanion intermediate**; elimination proceeds with **trans stereochemistry**, and C–N bond cleavage is likely rate-limiting (pqac-00000000, pqac-00000001) |
| Subcellular localization | **Cytosolic** enzyme; also functions in a compartmentalized **CAT1-ASS1-ASL-NOS** complex for arginine channeling to NOS (pqac-00000008, pqac-00000015, pqac-00000017) |
| Primary tissue expression | Expressed predominantly in **liver**; also present in **kidney (proximal tubules)**, brain, heart, muscle, skin, hematopoietic tissues, small intestine, pancreas, fibroblasts, and erythrocytes. Kidney is a major site of endogenous arginine synthesis (~60% net synthesis in adults) (pqac-00000008, pqac-00000009, pqac-00000012) |
| Pathway involvement | **Urea cycle:** supports ammonia detoxification/ureagenesis. **Citrulline-NO cycle:** regenerates arginine from citrulline to support nitric oxide synthesis by NOS (pqac-00000008, pqac-00000011, pqac-00000016) |
| Superfamily / family membership | Member of the **β-elimination / fumarate-lyase-related superfamily**, related to **δ-crystallin**, fumarase, aspartase, and adenylosuccinate lyase; highly conserved across bacteria to mammals (pqac-00000002, pqac-00000034, pqac-00000039) |
| Key catalytic residues | Frequently implicated catalytic residues include **H91, H162, K289, E296**; H162/K289/E296 are central to proton abstraction and charge-relay chemistry (pqac-00000001, pqac-00000002, pqac-00000037) |
| Disease association | Biallelic pathogenic variants cause **ASL deficiency (ASLD)**, also called **argininosuccinic aciduria (ASA)**, a urea-cycle disorder with hyperammonemia and broader systemic disease including neurocognitive and liver manifestations (pqac-00000003, pqac-00000020, pqac-00000026) |


*Table: This table summarizes the core molecular, structural, biochemical, and disease-related properties of human argininosuccinate lyase (ASL). It is useful as a compact reference for functional annotation and for connecting ASL’s enzymatic role to its pathway context and disease relevance.*