Effect of Fructose 2,6-bisphosphate on some Properties of Phosphofructokinase from Mucor rouxii

Abstract

Summary Mucor rouxii phosphofructokinase was stimulated by physiologically relevant concentrations of ammonium, phosphate and fructose 2,6-bisphosphate.Considerable stimulation was also obtained with potassium.The saturation curve for fructose 6-phosphate was slightly sigmoidal, but in the presence of fructose 2,6-bisphosphate or ammonium, hyperbolic kinetics were obtained.In addition, fructose 2,6-bisphosphate markedly stimulated enzyme activity at pH values above the optimum p H, increased the affinity of the enzyme for magnesium and ammonium ions, and relieved ATP-inhibition.Stimulation by fructose 2,6-bisphosphate was particularly effective when Hepes buffer was used for extraction and assay.In the presence of ammonium, a considerable increase of the reaction rate was observed, the optimum p H was shifted to p H 7.0, and inhibition by ATP and citrate was less pronounced.Furthermore, ammonium increased the affinity of phosphofructokinase for ATP and Mg, and enhanced the stimulatory effect of phosphate.No evidence for the involvement of cAMP in the regulation of phosphofructokinase activity was found.The specific activity of phosphofructokinase changed during spore development, the values for anaerobically growing yeast cells being consistently higher than those for aerobically growing mycelium.