Hydrodynamic studies on the quaternary structure of reacting yeast phosphofructokinase

Reacting yeast phosphofructokinase exhibits an octameric structure which is extremely stable towards changes in the protein concentration. This finding results from ultracentrifugation experiments performed in the presence of both substrates of phosphofructokinase at enzyme concentrations between 0.25 micrograms/ml and 1 mg/ml. The molecular mass of 870 kDa as determined by sucrose gradient centrifugation and the sedimentation coefficient of 22 S obtained by band centrifugation correspond with the undissociated octameric enzyme. Apparently, the concurrent presence of fructose 6-phosphate and magnesium-ATP counteracts enzyme dissociation by differential binding to the individual oligomeric species present in the equilibrium mixture of the enzyme.