Phosphoribosylaminoimidazole carboxylase

Phosphoribosylaminoimidazole carboxylase (or AIR carboxylase) is an enzyme 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:

5-aminoimidazole ribonucleotide + CO₂

\rightleftharpoons

5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H⁺

In plants and fungi

Phosphoribosylaminoimidazole carboxylase is a fusion protein in plants 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 Escherichia coli

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 bicarbonate to N5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP, and Pi.

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]

References

↑ Ealick SE, Stubbe J, Kappock TJ, Mathews II (1999). "Crystal structure of Escherichia coli PurE, an unusual mutase in the purine biosynthetic pathway". Structure. 7 (11): 1395–1406. doi:10.1016/S0969-2126(00)80029-5. PMID 10574791.
↑ Meyer E, Stubbe J, Kappock TJ, Osuji C (1999). "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". Biochemistry. 38 (10): 3012–3018. doi:10.1021/bi9827159. PMID 10074353.

External links

phosphoribosylaminoimidazole carboxylase at the US National Library of Medicine Medical Subject Headings (MeSH)
PAICS photo

This article incorporates text from the public domain Pfam and InterPro IPR000031

Purine metabolism

Anabolism

R5P→IMP:	Ribose-phosphate diphosphokinase Amidophosphoribosyltransferase Phosphoribosylglycinamide formyltransferase AIR synthetase (FGAM cyclase) Phosphoribosylaminoimidazole carboxylase Phosphoribosylaminoimidazolesuccinocarboxamide synthase IMP synthase

IMP→AMP:	Adenylosuccinate synthase Adenylosuccinate lyase reverse AMP deaminase

IMP→GMP:	IMP dehydrogenase GMP synthase reverse GMP reductase

Nucleotide salvage

Catabolism

Pyrimidine metabolism

Anabolism

CAD Carbamoyl phosphate synthase II Aspartate carbamoyltransferase Dihydroorotase

Dihydroorotate dehydrogenase Orotidine 5'-phosphate decarboxylase/Uridine monophosphate synthetase

CTP synthetase

Catabolism

Deoxyribonucleotides

Carbon-carbon lyases (EC 4.1)

4.1.1: Carboxy-lyases	Acetoacetate decarboxylase Adenosylmethionine decarboxylase Aromatic L-amino acid decarboxylase Glutamate decarboxylase Histidine decarboxylase Lysine decarboxylase Malonyl-CoA decarboxylase Ornithine decarboxylase Oxaloacetate decarboxylase Phosphoenolpyruvate carboxykinase Phosphoenolpyruvate carboxylase Phosphoribosylaminoimidazole carboxylase Pyrophosphomevalonate decarboxylase Pyruvate decarboxylase RuBisCO Uridine monophosphate synthetase/Orotidine 5'-phosphate decarboxylase Uroporphyrinogen III decarboxylase

4.1.2: Aldehyde-lyases	Fructose-bisphosphate aldolase Aldolase A Aldolase B Aldolase C 2-hydroxyphytanoyl-CoA lyase Threonine aldolase

4.1.3: Oxo-acid-lyases	Isocitrate lyase 3-hydroxy-3-methylglutaryl-CoA lyase

4.1.99: Other	Tryptophanase

Enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list)

This article is issued from Wikipedia - version of the 7/14/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.