IN-VIVO PHOSPHORYLATION OF PHOSPHOFRUCTOKINASE FROM THE BIVALVE MOLLUSK MYTILUS-GALLOPROVINCIALIS

The phosphorylation state of phosphofructokinase from the mantle tissu e of the facultative anaerobe mollusk Mytilus galloprovincialis was de termined by a back-phosphorylation technique. The incubation of intact mantle tissue with 8-bromoadenosine 3':5'-cyclic monophosphate increa sed significantly the phosphate content of phosphofructokinase, which indicates that the enzyme can be phosphorylated in vivo by endogenous cAMP-dependent protein kinase. The phosphate content of mussel phospho fructokinase changes significantly during the year, in agreement with the kinetic data that show a more active enzyme form in earlier autumn . These results suggest that cAMP-dependent phosphorylation of phospho fructokinase can be partially responsible for the observed glycolytic changes associated with the annual gametogenic cycle that takes place in the mantle tissue of the mollusk. On the contrary, no differences w ere observed between aerobic and 24-h hypoxic mussels with regard to t he phosphorylation state and the kinetic constants of phosphofructokin ase. This result is inconsistent with the hypothesis that phosphorylat ion of phosphofructokinase is involved in the glycolytic depression th at takes place during the long-term environmental hypoxia that the mol lusk can undergo.