Inorganic phosphate amplifies the effects of AMP and fructose-2,6-bisphosphate on yeast phosphofructokinase

Inorganic phosphate is an important regulator of yeast phosphofructokinase activity. In the absence of AMP and fructose-2,6-bisphosphate the dependence of enzyme activity on the concentration of inorganic phosphate is sigmoidal. AMP and fructose-2,6-bisphosphate increase the affinity of phosphofructokinase to inorganic phosphate. At low fructose-6-phosphate concentrations inorganic phosphate amplifies the activating effect of AMP and fructose-2,6-bisphosphate. Yeast phosphofructokinase is more sensitive to ATP inhibition in the absence of inorganic phosphate than in its presence. While in the absence of inorganic phosphate a definite ATP inhibition prevails even at high levels of AMP or fructose-2,6-bisphosphate, the ATP inhibition can be relieved by the cooperation of inorganic phosphate and fructose-2,6-bisphosphate. These effects of inorganic phosphate provide an explanation for the stimulation of glycolysis under anaerobic conditions by inorganic phosphate at unchanged concentrations of AMP and fructose-2,6-bisphosphate (Lagunas and Gancedo, Eur. J. Biochem. 137, 479-483 (1983)).