Metabolism of glucose in the crabs Cancer magister and Hemigrapsus nudus

Abstract

1. 1. The major blood carbohydrates of crabs include glucose 4, maltose, maltotriose, maltotretrose and glucose-6-phosphate. No trehalose could be detected. There are cosiderable amounts of acid-soluble glycoproteins. 2. 2. The maltose oligosaccharides show marked variation with diet and season; the glucose level is relatively stable. 3. 3. The changes in blood composition following feeding or injection of glucose suggest that glucose-6-phosphate is an intermediate in the synthesis of maltose oligosaccharides and that the latter are intermediates in glycogen synthesis. The carnon of labeled glucose appears first in glucose-6-phosphate, then in the oligosaccharides and finally in glycogen. 4. 4. The carbon of labeled maltose appears relatively early in glycogen but is not recovered from glucose within 48 hr. This appears to confirm the sequence postulated above. 5. 5. Glucose carbon is incorporated into chitin during the early poust-moult period, but not during intermoult. 6. 6. Glucose carbon is incorporated into mucopolysaccharide in the hepatopancreas at all stages but appears in the mucopolysaccharide of the integument only during the postmoult stages, not during the intermoult or premoult stages. 7. 7. Radioactive carbon from maltose appears in the respiratory CO 2 when only maltose is administered. If labeled maltose and unlabeled glucose are administered together, the fraction of maltose which appears as CO 2 decreases in proportion to the amount of glucose administered. 8. 8. A general hypothetical scheme of carbohydrate metabolism in crustaceans is presented and it is suggested that glycogenesis occurs through the UDPG-Synthetase system while glycogenolysis involves phosphorylase and the two paths are essentially separate.