The enzymes of pyrimidine biosynthesis in a range of parasitic protozoa and helminths

The activities of carbamoylphosphate synthase, aspartate transcarbamoylase, dihydroorotase, orotate phophoribosyl transferase and orotidine-5′-phosphate decarboxylase, five of the six enzymes of pyrimidine biosynthesis, have been measured in Crithidia fasciculata, Trypanosoma cruzi, Leishmania major, Trichomonas vaginalis, Eimeria tenella, Toxoplasma gondii, Plasmodium berghei, Fasciola gigantica, Schistosoma mansoni, Hymenolepis diminuts, Nippostrongylus brasiliensis and Trichuris muris. The majority of organism contained all five enzyme activities. However, in T. vaginalis on;y carbamoylphosphate synthetase activity and in E. tenella only orotate phosphoribosyl transferase and orotidine-5′-phosphate decarboxylase activities could be detected. It appears therefore that the ability to synthesise pyrimidines by the de novo route is probably both common and wide-spread amongst parasitic organisms.