EFFECTS OF ANOXIA ON THE ACTIVITIES OF PYRUVATE-KINASE AND PHOSPHOENOLPYRUVATE CARBOXYKINASE, AND THE PRODUCTION OF LACTATE AND SUCCINATE IN THE INTERTIDAL PULMONATE ONCHIDIUM-TUMIDIUM

Onchidium tumidium, an intertidal pulmonate, has evolved to depend mai nly on the formation of succinate, rather than lactate and opines, to survive in anoxia. For our study O. tumidum were collected from the mu d flats of the mangrove swamp at Mandai, Singapore between 1988 and 19 91. After 24 h of anoxic exposure, the lactate and succinate contents of the anoxic individuals were approximately 10 and 150 times, respect ively, the corresponding values of the normoxic individuals. Alanine a nd acetate accumulations also occurred during anoxia, though to a much lesser extent. No propionate or octopine was detected. The depletion in aspartate content in O. tumidium could not account for the amount o f succinate accumulated during anoxia. The succinate formed might have originated from glycogen involving the flow of carbon through the pho sphoenolpyruvate (PEP) branch point of glycolysis. In support of such a hypothesis, results indicate that there was a decrease in the affini ty of pyruvate kinase from O. tumidium exposed to 24 h of anoxia to PE P to facilitate succinate formation through phosphoenolpyruvate carbox ykinase (PEPCK). In comparison, the affinity of PEPCK from O. tumidium exposed to anoxia to PEP was apparently unaltered.