THE ROLE OF FRUCTOSE 2,6-BISPHOSPHATE IN THE REGULATION OF MARINE MUSSELS (MYTILUS-GALLOPROVINCIALIS AND MYTILUS-EDULIS) GLYCOLYSIS GLUCONEOGENESIS

1. Fru-2,6-P2 plays an important modulating role in the glycolysis/gluconeogenesis of sessile marine molluscs, indicating by its content the change in both the flow direction and the glycogen reserves. 2. PFK-1 is activated, while FBPase-1 is inhibited by Fru-2,6-P2. The phosphoester synergically enhances the effect caused by AMP on both enzymes. 3. As in mammals, the different PFK-2 from marine molluscs are bifunctional enzymes with the hydrolytic FBPase-2 activity. The reversible covalent modification of PFK-2/FBPase-2 by phosphorylation/dephosphorylation displays different responses according to the source of the enzyme. 4. A low temperature sea-water and the presence of glucose increase the concentration of Fru-2,6-P2 parallel to the activation of the glycolytic pathway; whereas alanine and propionate, promoters of glyconeogenesis, reduce the Fru-2,6-P2 content. 5. The concentration of Fru-2,6-P2 in mantle and hepatopancreas presents seasonal variations with peaks in winter and the low values in both spring and summer; these fluctuations are parallel to the feeding-breeding cycle. 6. The variations in the concentration of Fru-2,6-P2 during the physiological hypoxia or during anoxia are discussed, on the basis of processes of reversible phosphorylation/dephosphorylation of PFK-2/FBPase-2.