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Pyrimidine and purine nucleotides, the constituents of nucleic acids, are essential for cellular proliferation in living organisms, and synthesized through the de novo or salvage biosynthetic pathway. It is of interest, therefore, to clarify the details of synthetic pathways of nucleotides in parasitic helminths, since their nutritional requirements entirely depend upon the hosts. Such investigation may provide a new biochemical approach for a better understanding of the host-parasite relationship, especially in regard to the metabolic adaptation of parasites to the hosts. Senft et al.l~ reported that the de novo pathway for the synthesis of purine nucleotides was not operative in schistosomes while salvage mechanism was actually in operation to fulfill the purine requirement of the fluke. It has been generally accepted that glutamine-dependent carbamoyl-phosphate synthetase (CPSase II) catalyzes the first step of pyrimidine biosynthetic pathway and plays a key role in the control of the pathway in animal systems.2~-5) On the other hand, little is known about pyrimidine synthesis in parasitic helminths. The synthesis of carbamoyl-phosphate had been explored in some helminths but the results were not enough to claim the presence of the responsible enzyme, although aspartate transcarbamoylase (ATCase) was demonstrated in these parasites.° The present paper deals with the demonstration of CPSase II in Ascaris ovary and its catalytic and regulatory properties. Materials and methods. 1) Materials. Ascaris lumbricoides var. suis were collected from swine intestines at a slaughter house in Tokyo. The ovaries were separated from the dissected worm and thoroughly washed with the cold Locke's solution. 2) Purification o f CPSase II. CPSase II was purified about 20-fold from 105,000 g supernatant of Ascaris ovary homogenates by

Glutamine-dependent Carbamoyl-phosphates Synthetase in Ascaris Ovary and its Regulatory Properties