The inhibition of Pfk A by PEP (A,B), citrate (C,D), and GDP (E,F). Plots of the inhibitions with F6P varied and ATP fixed at 1 mM (left diagrams: A,C,E) and the inhibitions with ATP varied and F6P fixed at 1 mM (right diagrams: B,D,F). The data were fitted to Equations (2) and (4).