PATHWAYS OF PYRIMIDINE NUCLEOTIDE BIOSYNTHESIS IN GRAVID ANGIOSTRONGYLUS-CANTONENSIS

The incorporation of radioactive precursors into pyrimidine nucleotide s via de novo and salvage pathways was measured in gravid Angiostrongy lus cantonensis by HPLC and thin-layer chromatography. C-14-labelled o rotate, uridine, uracil and deoxyuridine were traced to UMP, UDP, UTP, UDP-glucose, dTMP, CMP, CDP and CTP. H-3-labelled cytidine was also i ncorporated into both uracil and cytosine nucleotides in a ratio of 2: 1. Cytosine was a major end-product for all the precursors. Cytosine n ucleotides were probably formed from UTP by the action of CTP syntheta se whose activity in crude cell-free extract was 31.5 +/- 4.9 pmol min -1 (mg protein)-1. It was dependent on glutamine, ATP and GTP and was inhibited by CTP. The total amount of pyrimidine nucleotides formed fr om uridine was 3 times of that from uracil. The presence of uracil in the metabolism of uridine indicates that UMP is formed by uracil phosp horibosyltransferase as well as by uridine kinase. UMP is a key interm ediate for cytidylate and thymidylate biosynthesis in the gravid worms .