FIGURE 11.

Linkage relationship between the binding saturation fractions and the free concentration of ligands. The parameter γ (the derivative of the saturation fraction of FNR with a given ligand with respect to the free concentration of ligands NADP⁺ and Fd or Fld) is plotted as a function of the free concentration of the ligands: (A) ∂F_b,Fd/∂ln[NADP⁺] or ∂F_b,NADP+/∂ln[Fd] for FNRwt; (B) ∂F_b,Fld/∂ln[NADP⁺] or ∂F_b,NADP+/∂ln[Fld] for FNRwt; and (C) ∂F_b,Fld/∂ln[NADP⁺] or ∂F_b,NADP+/∂ln[Fld] for FNR_Y303S. (D) The parameter ɛ (the derivative of the saturation fraction of FNR with a given ligand with respect to the saturation fraction of the other ligand) is plotted as a function of the free ligand concentration: ∂F_b,Fd/∂F_b,NADP+ for FNRwt (solid line); ∂F_b,Fld/∂F_b,NADP+ for FNRwt (dashed line); and ∂F_b,Fld/∂F_b,NADP+ for FNR_Y303S (dotted line). Since there is negative cooperativity, γ and ɛ are represented in absolute value (Eq. 13).