Precursors of pyrimidine nucleotide biosynthesis for gravid Angiostrongylus cantonensis (Nematoda: Metastrongyloidea).

Gravid Angiostrongylus cantonensis can utilize radiolabelled bicarbonate, orotate, uracil, uridine and cytidine but not cytosine, thymine and thymidine for the synthesis of RNA and DNA. In cell-free extracts of the worm, a phosphoribosyltransferase was shown to convert orotate to OMP and uracil to UMP. A similar reaction was not observed with cytosine and thymine. Uridine was readily phosphorylated by a kinase but a similar reaction for thymidine and deoxyuridine was not found. Cytidine could be phosphorylated by a kinase or be deaminated by a deaminase to uridine. No deaminase for cytosine was detected. There was also no phosphotransferase activity for pyrimidine nucleosides in the cytosolic or membrane fractions. Pyrimidine nucleosides were, in general, converted to the bases by a phosphorylase reaction but only uracil and thymine could form nucleosides in the reverse reaction. The activity of thymidylate synthetase was also measured. These results indicate that the nematode synthesizes pyrimidine nucleotides by de novo synthesis and by utilization of uridine and uracil and that cytosine and thymine nucleotides are formed mainly through UMP. The thymidylate synthetase reaction appears to be vital for the growth of the parasite.