A comparison of the influence of potassium and ammonium ions on the phosphofructokinases from rabbit muscle and rat erythrocytes.

Phosphofructokinases from rat erythrocytes and rabbit muscle have been compared in their kinetic behavior with respect to monovalent cation activation and ATP inhibition. Both ammonium and potassium ions affect the muscle enzyme in a two-fold manner: they act both as activators and effectors. On the other hand only ammonium exerts the two-fold effects on the erythrocyte enzyme, while the potassium ions activate without affecting cooperativity. The lower ATP inhibition of muscle phosphofructokinase may be partially explained by the action of potassium ions on the cooperative behavior of the enzyme. The differences between the phosphofructokinases from erythrocytes and muscle in the potassium type-II activation and ATP inhibition represent an organ specifity. Furthermore, the inhibition constants for 2, 3-bisphosphoglycerate differ by 10-fold between the two enzymes.