Structure and control of phosphofructokinase from Bacillus stearothermophilus.

The allosteric enzyme phosphofructokinase binds its substrate fructose-6-phosphate between two subunits of the tetramer, and allosteric effectors between another pair of subunits. The effector binding site accommodates both the activator and the inhibitor. The substrate cooperativity and allosteric control are mediated by these ligand bridges between subunits.