Influence of free Mg2+ on the kinetics of human erythrocyte phosphofructokinase.

The influence of Mg2+ on the reaction catalyzed by human erythrocyte phosphofructokinase has been investigated using kinetic methods. The catalytic activity of PFK is dependent upon the presence of Mg2+ which constitutes with ATP the true Mg-ATP2- substrate. Free Mg2+ has no influence on the affinity of the enzyme for Mg-ATP2- substrate. Erythrocyte PFK is more inhibited by ATP4- and uncomplexed citrate than it is by Mg-ATP2- and Mg-citrate. Free Mg2+ relieves the MgATP2- and Mg-citrate inhibition under conditions where free ATP4-is negligible. We can assume that uncomplexed Mg2+ acts as positive effector by direct binding to the enzyme. These results emphasize the role of Mg2+ in the regulation of PFK activity in the erythrocyte.