Purification and properties of phosphofructokinase 2/fructose 2,6‐bisphosphatase from chicken liver and from pigeon muscle

Phosphofructokinase 2 and fructose 2,6‐bisphosphatase extracted from either chicken liver or pigeon muscle co‐purified up to homogeneity. The two homogeneous proteins were found to be dimers of relative molecular mass ( M r ) close to 110000 with subunits of M r 54000 for the chicken liver enzyme and 53000 for the pigeon muscle enzyme. The latter also contained a minor constituent of M r 54000. Incubation of the chicken liver enzyme with the catalytic subunit of cyclic‐AMP‐dependent protein kinase in the presence of [γ‐ 32 P]ATP resulted in the incorporation of about 0.8 mol phosphate/mol enzyme. Under similar conditions, the pigeon muscle enzyme was phosphorylated to an extent of only 0.05 mol phosphate/mol enzyme and all the incorporated phosphate was found in the minor 54000‐ M r constituent. The maximal activity of the native avian liver phosphofructokinase 2 was little affected by changes of pH between 6 and 10. Its phosphorylation by cyclic‐AMP‐dependent protein kinase resulted in a more than 90% inactivation at pH values below 7.5 and in no or little change in activity at pH 10. Intermediary values of inactivation were observed at pH values between 8 and 10. Muscle phosphofructokinase 2 had little activity at pH below 7 and was maximally active at pH 10. Its partial phosphorylation resulted in a further 25% decrease of its already low activity measured at pH 7.1 and in a negligible inactivation at pH 8.5. Phosph oenol pyruvate and citrate inhibited phosphofructokinase 2 from both origins non‐competitively. The muscle enzyme and the phosphorylated liver enzyme displayed much more affinity for these inhibitors than the native liver enzyme. Fructose 2,6‐bisphosphatase from both sources had about the same specific activity but only the chicken liver enzyme was activated about twofold upon incubation with ATP and cyclic‐AMP‐dependent protein kinase. All enzyme forms were inhibited by fructose 6‐phosphate and this inhibition was released by inorganic phosphate and by glycerol 3‐phosphate. Both liver and muscle fructose 2,6‐bisphosphatases formed a 32 P‐labeled enzyme intermediate when incubated in the presence of fructose 2,6‐[2‐ 32 P]bisphosphate.