THE METABOLISM OF PYRIMIDINE AND PURINE IN SCHISTOSOMA JAPONICUM

Experiments on the pyrimidine metabolism in Schistosoma japonicum demonstrated that labelled bicarbonate, orotic acid and uracil are all incorporated into the nucleic acids of worms. This indicates that carbamoyl phosphate synthetase II-aspartate carbamoyl transferase-dihydroorotase complex, dihydroorotate dehydrogenase as well as orotate phosphoribosyl transferase-orotidylate decarboxylase complex do exist in S japonicum. S japonicum possesses not only all the enzymes of the pyrimidine de novo pathway but also the capacity of salvaging the preformed pyrimidines. The effect of schistosomicides (niridazole and anoscanate) on the pyrimidine de novo pathway in vivo has also been studied. It is suggested that the orotate phosphoribosyl transferase (orotidylate decarboxylase complex) is a vulnerable point which might be attacked by chemotherapeutic agents. The adenosone triphosphatase of tegument in S japonicum has been investigated. The specific activities of male and female worms were 17.3±3.8 and 17.0±2.5 μ moles Pi/hr/mg protein at 37 C respectively, and the km of the former was 6.25×10-4M. Mg++ and Mn++, could activate the tegumental ATPase markedly, whereas Ca+ did exhibit a weak stimulatory effect. The tegument was also capable of decomposing ADP, AMP, GTP and B-glycerophosphate to various extent.