Gluconeogenesis in hepatopancreas of Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets

Abstract

The capacity for glucose synthesis in Chasmagnathus granulata hepatopancreas, associated with phosphoenolpyruvate carboxykinase activity, argues in favor of this tissue as a site for gluconeogenesis. In order to obtain more information on the gluconeogenic capacity in crabs, we investigated the effects of different diets on the incorporation of ¹⁴C-alanine or ¹⁴C-lactic acid into glucose in Chasmagnathus granulata hepatopancreas, as well as on the phosphoenolpyruvate carboxykinase activity in this organ. In contrast to what occurs in vertebrates, in Chasmagnathus granulata, the intrinsic capacity of the hepatopancreas to synthetize glucose from alanine or lactic acid, and its phosphoenolpyruvate carboxykinase activity, was not influenced by high-protein or carbohydrate diets. The amount of labelled glucose recovered from ¹⁴C-alanine was significantly higher than that recovered from ¹⁴C-lactic acid, and 40 mM of alanine is not a saturated concentration for the gluconeogenic pathway. Phosphoenolpyruvate carboxykinase activity was detected into the mitochondrial (10,000 × g) and cytosol (100,000 × g) fractions. The data suggest that gluconeogenesis from ¹⁴C-alanine in the hepatopancreas from Chasmagnathus granulata fed a high-protein or carbohydrate-rich diet is equally subject to end-point inhibition by glucose, as has been found in vertebrates.