 The step of histidine biosynthesis is the condensation of ATP and PRPP by ATP-phosphoribosyl transferase, the rate determining enzyme.Histidine biosynthesis is carefully regulated by feedback inhibition/

R5P can be converted to adenosine diphosphate ribose, which binds and activates the TRPM2 ion channel.The reaction is catalyzed by ribose-5-phosphate adenylyltransferase

Diseases have been linked to R5P imbalances in cells.