View source for Phosphoribosylaminoimidazole carboxylase

{{Short description|Enzyme involved in purine synthesis}}
{{infobox enzyme
| Name       = phosphoribosylaminoimidazole carboxylase
| EC_number  = 4.1.1.21
| CAS_number = 9032-04-6
| GO_code    = 0004638
| image      = 2h31a.jpg
| width      = 270
| caption    = Phosphoribosylaminoimidazole carboxylase octamer, Human
| name       = Phosphoribosylaminoimidazole carboxylase
}}
{{infobox protein
| Name       = phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase
| caption    = 
| image      = 
| width      = 
| HGNCid     = 8587
| Symbol     = PAICS
| AltSymbols = PAIS
| EntrezGene = 10606
| OMIM       = 172439
| RefSeq     = NM_006452
| UniProt    = P22234
| PDB        = 
| ECnumber   = 4.1.1.21
| Chromosome = 4
| Arm        = p
| Band       = ter
| LocusSupplementaryData = -q21
}}

The [[enzyme]] '''Phosphoribosylaminoimidazole carboxylase''', or '''AIR carboxylase''' ({{EnzExplorer|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|5'-phosphoribosyl-4-carboxy-5-aminoimidazole]] ("CAIR") as described in the reaction:

:5-aminoimidazole ribonucleotide + CO<sub>2</sub> <math>\rightleftharpoons</math> 5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H<sup>+</sup>

==In plants and fungi==
Phosphoribosylaminoimidazole carboxylase is a [[fusion protein]] in [[plant]]s 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.<ref name="PUB00016906">{{cite journal |doi=10.1016/S0969-2126(00)80029-5 |vauthors=Ealick SE, Stubbe J, Kappock TJ, Mathews II |title=Crystal structure of Escherichia coli PurE, an unusual mutase in the purine biosynthetic pathway |journal=Structure |volume=7 |issue=11 |pages=1395–1406 |year=1999 |pmid=10574791|doi-access=free }}</ref>

==In ''Escherichia coli''==
In the [[bacteria|bacterium]] ''[[Escherichia coli]]'' the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.

PurK, [[N5-carboxyaminoimidazole ribonucleotide synthetase|''N''5-carboxyaminoimidazole ribonucleotide synthetase]], catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), [[Adenosine triphosphate|ATP]], and [[bicarbonate]] to ''N''5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), [[Adenosine diphosphate|ADP]], and [[phosphate]].

PurE, [[N5-carboxyaminoimidazole ribonucleotide mutase|''N''5-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.<ref name="PUB00016905">{{cite journal |vauthors=Meyer E, Stubbe J, Kappock TJ, Osuji C |title=Evidence for the direct transfer of the carboxylate of N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) to generate 4-carboxy-5-aminoimidazole ribonucleotide catalyzed by ''Escherichia coli'' PurE, an N5-CAIR mutase |journal=Biochemistry |volume=38 |issue=10 |pages=3012–3018 |year=1999 |pmid=10074353 |doi=10.1021/bi9827159}}</ref>

==References==
{{reflist}}

==External links==
* {{MeshName|phosphoribosylaminoimidazole+carboxylase}}
*[http://astrojan.zz.mu/protein/pictures/paics.jpg PAICS photo] {{Webarchive|url=https://web.archive.org/web/20171222053540/http://astrojan.zz.mu/protein/pictures/paics.jpg |date=2017-12-22 }}

{{InterPro content|IPR000031}}
{{Nucleotide metabolism enzymes}}
{{Carbon-carbon lyases}}
{{Enzymes}}
{{Portal bar|Biology|border=no}}

[[Category:EC 4.1.1]]


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