Overview Phosphoribosyl pyrophosphate (PRPP) sugar building block formed in nucleotide synthesis added to nitrogenous base to form nucleoside formed from ribose-5-phosphate product of pentose phosphate shunt ATP + ribose-5-phosphate = PRPP + AMP catalyzed by PRPP synthetase once PRPP is made it can add to either a de novo or salvaged base Pyrimidine pathway diagram important enzymes carbamoyl phosphate synthetase-2 login to view 2 more bullets ribonucleotide reductase login to view 5 more bullets thymidylate synthase login to view 2 more bullets dihydrofolate reductase login to view 6 more bullets deficiency orotic aciduria login to view 14 more bullets purine pathway diagram insufficient capacity in most cells important enzymes PRPP amidotransferase login to view 4 more bullets note: base of inosine = hypoxanthine