PHOSPHOFRUCTOKINASE FROM THE POSTERIOR GILLS OF THE EURYHALINE CRAB, ERIOCHEIR-SINENSIS - EVIDENCE FOR ITS REGULATION BY PHOSPHORYLATION

Phosphofructokinase from the posterior gills of the euryhaline crab Eriocheir sinensis acclimated to freshwater is likely regulated in part via phosphorylation induced by endogenous cyclic nucleotide-dependent protein kinases. Phosphofructokinase from gill extracts devoid of low molecular weight compounds by chromatography through a PD10 Sephadex column, incubated in the presence of cAMP or cGMP protein kinases activators (cAMP or cGMP, Mg-ATP and Mg2+), shows an increased catalytic activity. This treatment is accompanied by P-32 incorporation into the proteins immuno-precipitated with anti-mammalian phosphofructokinase polyclonal antibodies cross-reacting with the analog crustacean enzyme. Our results indicate that the covalent modification induced by these nucleotide-dependent protein kinases activates the glycolytic enzyme by increasing its affinity for its substrate and, when the activation is specifically due to cAMP-dependent protein kinases, by also reducing the homotropic cooperativity between its multiple substrate binding sites.