In enzymology, a 5-(carboxyamino)imidazole ribonucleotide synthase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are ATP, 5-amino-1-(5-phospho-D-ribosyl)imidazole ("AIR"), and HCO<sub>3</sub><sup>−</sup>, whereas its 3 products are ADP, phosphate, and 5-carboxyamino-1-(5-phospho-D-ribosyl)imidazole.
This enzyme belongs to the family of ligases, specifically those forming generic carbon-nitrogen bonds. The systematic name of this enzyme class is 5-amino-1-(5-phospho-D-ribosyl)imidazole:carbon-dioxide ligase (ADP-forming).