Regulation of Phosphofructokinase from Aspergillus Niger: Effect of Fructose 2,6-Bisphosphate on the Action of Citrate, Ammonium Ions and AMP

The role of fructose 2,6-bisphosphate in the regulation of glycolysis in the citric acid accumulating fungus Aspergillus niger was investigated. Fructose 2,6-bisphosphate stimulated the activity of partially purified phosphofructokinase by increasing the affinity of the enzyme for fructose 6-phosphate and relieving inhibition by ATP. Fructose 2,6-bisphosphate acted synergistically with AMP, but not with NH+ 4 ions, which otherwise also activate phosphofructokinase. Fructose 2,6-bisphosphate also partially antagonized citrate inhibition of phosphofructokinase; complete deinhibition against high (5 mm) concentrations of citrate (as occur during citric acid accumulation), however, required the simultaneous presence of fructose 2,6-bisphosphate (0·1 μm). AMP (0·1 μm) and NH+ 4 ions (20 mm).