Properties of phospho and dephospho forms of muscle phosphofructokinase

Rabbit muscle phosphofructokinase, phosphorylated either in vivo or in vitro, can be dephosphorylated by bovine intestinal alkaline phosphatase. Small but consistent differences in the allosteric regulatory properties of the phospho and dephospho forms are seen with the pattern in the direction of the phospho form being more inhibited. In vitro phosphorylated phosphofructokinase is more sensitive to allosteric inhibition by ATP and citrate and less sensitive to activation by AMP, glucose 1,6-bisphosphate, and inorganic phosphate than untreated or dephosphorylated phosphofructokinase. Fructose 2,6-bisphosphate activates muscle phosphofructokinase with a K alpha less than 1 microM. The phospho-enzyme is less sensitive to activation by the bisphosphate. On the other hand, there are no differences in the sedimentation properties under a variety of conditions or in the stability of phosphorylated and dephosphorylated phosphofructokinases as shown by sucrose density gradient centrifugation and low pH inactivation, respectively.