This is a family of bifunctional enzymes catalyzing the last two steps in de novo purine biosynthesis. The bifunctional enzyme is found in both prokaryotes and eukaryotes. The second last step is catalyzed by 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase EC:126.96.36.199 (AICARFT), this enzyme catalyzes the formylation of AICAR with 10-formyl-tetrahydrofolate to yield FAICAR and tetrahydrofolate. This is catalyzed by a pair of C-terminal deaminase fold domains in the protein, where the active site is formed by the dimeric interface of two monomeric units. The last step is catalyzed by the N-terminal IMP (Inosine monophosphate) cyclohydrolase domain EC:188.8.131.52 (IMPCHase), cyclizing FAICAR (5-formylaminoimidazole-4-carboxamide ribonucleotide) to IMP.