Inosine monophosphate synthase

Bifunctional purine biosynthesis protein PURH is a protein that in humans is encoded by the ATIC gene.
ATIC encodes an enzyme which generates inosine monophosphate from aminoimidazole carboxamide ribonucleotide.
It has two functions:

- 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase

In this step, AICA ribonucleotide is formylated, with the formyl group being transferred from the cofactor 5,10-methylenetetrahydrofolate.

- IMP cyclohydrolase

This enzyme forms the purine ring of inosine monophosphate by dehydration and cyclisation of N-formyl AICA ribonucleotide.