 The ninth is catalyzed by phosphoribosylaminoimidazolecarboxamide formyltransferase.AICAR + fTHF → FAICAR + THF

The last step is catalyzed by Inosine monophosphate synthase.FAICAR → IMP + H2O

In eukaryotes the second, third, and fifth step are catalyzed by trifunctional purine biosynthetic protein adenosine-3, which is encoded by the GART gene.