Phosphoribosylaminoimidazole Carboxylase (PAICS)

PAICS is an enzyme involved in nucleotide synthesis. It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole ("AIR") into 5-phosphoribosyl-4-carboxy-5-aminoimidazole ("CAIR"). PurK, N5-carboxyaminoimidazole ribonucleotide (N5_CAIR) synthetase, catalyzes the conversion of 5-aminoimidazole ribonucleotide (AIR), ATP, and bicarbonate to N5-CAIR, ADP, and Pi.PurE 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.Phosphoribosylaminoimidazole carboxylase is a fusion protein in plants and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.