Regulation of the Level of Key Enzymes of Glycolysis and Gluconeogenesis in Liver

Diets rich in fructose, glycerol, or both were fed to normal and diabetic rats, and the activities of enzymes which catalyze irreversible steps of glycolysis and gluconeogenesis were studied in liver. With these diets, rich in precursors of triosephosphates, the activities of glucose‐6‐phosphatase and pyruvate kinase in liver were high, while those of glucokinase and phosphoenolpyruvate carboxykinase were low. A metabolic bifurcation to glycolysis and gluconeogenesis, below and above the triosephosphates level respectively, has then been shown to be easily maintained in liver. It is suggested that the induction of glucokinase and pyruvate kinase in diabetic animals after insulin administration is a sequential process that involves hormonal induction of glucokinase by insulin and secondary metabolite induction of the L isoenzyme of pyruvate kinase by some glycolytic intermediate. The occurrence of independent mechanisms for the regulation in liver of the activity of enzymes which catalyze irreversible steps of glycolysis and gluconeogenesis affords a valuable metabolic plasticity.