Metabolism of glucose and glycogen in Limulus polyphemus in vivo

1. As much as 70% of Tritium administered on C-6 of glucose is excreted as 3H2O within 3 hr, showing an extensive, rapid glycolytic degradation of glucose in Limulus. About 80% of the 14C found in Limulus blood one hour after injection of glucose-14C is in the anionic fraction. 2. Preferential loss of carbon from C-1 of glucose prior to incorporation into glycogen in paired in vivo experiments indicates a significant occurrence of the oxidative (pentose phosphate) pathway of glucose metabolism. 3. Glucose is more rapidly and extensively incorporated into glycogen of muscle than into that of hepatopancreas, indicative of the relative importance of muscle in metabolic turnover in Limulus. Maximum incorporation into leg muscle glycogen of a large individual Limulus was seen at about 4-6 hr after a single injection of glucose-14C. 4. Little gluconeogenesis from lactate or pyruvate was observed. 5. The glucose of Limulus blood, occurring normally at levels of only about 3-5 mg per 100 ml, undergoes rapid metabolic changes and utilization.