FIG 1.

Pyrimidine synthesis and salvage pathways in Toxoplasma gondii. The six-step de novo pyrimidine synthesis pathway (red) and the pyrimidine salvage enzyme pathway (blue) show both pathways produce uridine-5′-monophosphate (UMP) (boxed). Intermediate metabolites are shown (phosphoribosyl-1-pyrophosphate [PRPP]). (Top) The biosynthetic enzymes mediating each step of the de novo pathway are carbamoyl phosphate synthetase II (CPSII), aspartate carbamoyltransferase (ACT), dihydroorotase (DHO), dihydroorotate dehydrogenase (DHODH), orotate phosphoribosyltransferase (OPRT), and orotidine-5′-monophosphate (OMP) decarboxylase (OMPDC). (Bottom) The pyrimidine salvage enzymes mediating each step of the salvage pathway are cytidine deaminase (CTD), uridine phosphorylase (UP), and uracil phosphoribosyltransferase (UPRT).