Fructose 2,6-bisphosphate metabolism in Ehrlich ascites tumour cells

Abstract

Cancer cell energy metabolism is characterized by a high glycolytic rate, which is maintained under aerobic conditions. In Ehrlich ascites tumour cells, the concentration of fructose 2,6-bisphosphate (Fru-2,6-P ₂), the powerful activator of 6-phosphofructo-1-kinase, is tenfold increased. The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2), synthesizing and degrading Fru-2,6-P ₂, was characterized. The molecular mass is 120 kDa. The dependence of PFK-2 activity on the substrate concentrations is hyperbolic (K _m for Fru-6-P=0.09 mM;K _m for ATP=0.7 mM), while the dependence of the FBPase-2 activity on the concentrations of Fru-2,6-P ₂ is sigmoidal (K _0.5 for Fru-2,6-P ₂=4μM). The PFK-2/FBPase-2 activity ratio is 1. PFK-2 activity is inhibited by citrate (I _0.5=0.17 mM) and phosphoenolpyruvate (I _0.5=0.08 mM) but only weakly by glycerol 3-phosphate (I _0.5=1.57 mM). In contrast to the liver enzyme, the activity of tumour PFK-2/FBPase-2 is not influenced by the action of cAMP-dependent protein kinase. The kinetic properties as well as ion-exchange chromatography pattern differ from their normal counterparts in liver and muscle. The properties are likely to contribute to the maintenance of the high glycolytic rate in these tumour cells.