The enzymes that catalyse the salvage of pyrimidines in Fasciola hepatica, Moniezia expansa and Dirofilaria immitis have been surveyed. Cytidine deaminase, catabolic phosphorylase, nucleotidase, nucleoside kinase and uracil phosphoribosyltransferase were all detected where as cytosine deaminase and nucleosidase were not found- Anabolic phosphorylase was found to be active towards thymine in F. hepatica and towards thymine and Uracil in M. expansa and D. immitis. The results suggest that in these parasitic helminths the main route of pyrimidine nucleotide synthesis is through either the action of kinases or through uracil phosphoribosyltransferase. Thymidylate synthesis activity was also detected in these parasites and may be use as target for chemotherapeutic attack.
The levels of orotate phosphoribosyltransferase activities detected in the extracts of all the species suggests that these helminths have the ability of synthesizing pyrimidine nucleotides through de novo pathway. The results also suggest that the nucleotidase may be persent on the external surface of these parasites.