Argininosuccinate synthetase
| Argininosuccinate synthetase | |||||||||
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Crystallographic structure of human argininosuccinate synthetase.
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| Identifiers | |||||||||
| EC number | 6.3.4.5 | ||||||||
| CAS number | 9023-58-9 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / EGO | ||||||||
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| Search | |
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| PMC | articles |
| PubMed | articles |
| NCBI | proteins |
| Argininosuccinate synthetase 1 | |
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| Identifiers | |
| Symbol | ASS1 |
| Entrez | 445 |
| HUGO | 758 |
| OMIM | 603470 |
| RefSeq | NM_000050 |
| UniProt | P00966 |
| Other data | |
| EC number | 6.3.4.5 |
| Locus | Chr. 9 q34.1 |
| Argininosuccinate synthetase | |||||||||
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crystal structure of thermus thermophilus hb8 argininosuccinate synthetase in complex with atp and citrulline
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| Identifiers | |||||||||
| Symbol | Arginosuc_synth | ||||||||
| Pfam | PF00764 | ||||||||
| Pfam clan | CL0039 | ||||||||
| InterPro | IPR001518 | ||||||||
| PROSITE | PDOC00488 | ||||||||
| SCOP | 1kp2 | ||||||||
| SUPERFAMILY | 1kp2 | ||||||||
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| Available protein structures: | |
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| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
Argininosuccinate synthase or synthetase (ASS; EC 6.3.4.5) is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate.
ASS is responsible for the third step of the urea cycle and one of the reactions of the citrulline-NO cycle.
The gene that encodes for this enzyme, ASS, is located on chromosome 9. In humans, ASS is expressed mostly in the cells of liver and kidney. The expressed ASS gene is at least 65 kb in length, including at least 12 introns.
In the first step of the catalyzed reaction, citrulline attacks the α-phosphate of ATP to form citrulline adenylate, a reactive intermediate. The attachment of AMP to the ureido (urea-like) group on citrulline activates the carbonyl center for subsequent nucleophilic attack. This activation facilitates the second step, in which the α-amino group of aspartate attacks the ureido group. Attack by aspartate is the rate-limiting step of the reaction. This step produces free AMP and L-argininosuccinate.
Thermodynamically, adenylation of the citrulline ureido group is more favorable than the analogous phosphorylation. Additionally, attack by citrulline at the α-phosphate of ATP produces an equivalent of pyrophosphate, which can be hydrolyzed in a thermodynamically favorable reaction to provide additional energy to drive the adenylation.
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