Figure 4.

Solutions for the extended model with 5 intermediate metabolites X₁, …, X₅. The points represent the optimal enzyme levels of the two cells, while the gray bars are the membrane permeabilities (D_i) for the intermediate metabolites. In each panel, the P metabolite and one of the intermediate metabolites X_i [i = 1, 3, and 5 in panels (A–C), respectively] is allowed to permeate through the membrane (D = 15), while all others were not (D = 10⁻³). In these conditions, the pathway is split in correspondence of the permeable intermediate metabolite. Other settings: K_eq = 4/3 for all reversible reactions (all but the one catalyzed by the E_P enzyme). Inhibition constant: K_I = 1/10; the concentration of [S] = 20.