The enzyme Phosphoribosylaminoimidazole carboxylase, or AIR carboxylase (EC 4.1.1.21) is involved in nucleotide biosynthesis and in particular in purine biosynthesis. It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole ("AIR") into 5'-phosphoribosyl-4-carboxy-5-aminoimidazole ("CAIR") as described in the reaction:
| Phosphoribosylaminoimidazole carboxylase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Phosphoribosylaminoimidazole carboxylase octamer, Human
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| Identifiers | |||||||||
| EC no. | 4.1.1.21 | ||||||||
| CAS no. | 9032-04-6 | ||||||||
| 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 / QuickGO | ||||||||
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| phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase | |||||||
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| Identifiers | |||||||
| Symbol | PAICS | ||||||
| Alt. symbols | PAIS | ||||||
| NCBI gene | 10606 | ||||||
| HGNC | 8587 | ||||||
| OMIM | 172439 | ||||||
| RefSeq | NM_006452 | ||||||
| UniProt | P22234 | ||||||
| Other data | |||||||
| EC number | 4.1.1.21 | ||||||
| Locus | Chr. 4 pter-q21 | ||||||
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5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H+Phosphoribosylaminoimidazole carboxylase is a fusion proteininplants and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.
The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme.[1]
In the bacterium Escherichia coli the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.
PurK, N5-carboxyaminoimidazole ribonucleotide synthetase, catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), ATP, and bicarbonatetoN5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP, and phosphate.
PurE, N5-carboxyaminoimidazole ribonucleotide mutase, converts N5-CAIR to CAIR, the sixth step of de novo purine biosynthesis. In the presence of high concentrations of bicarbonate, PurE is reported able to convert AIR to CAIR directly and without ATP. Some members of this family contain two copies of this domain.[2]
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