Fig. 6.

Apparent cooperativity of steady-state Z response as a function of X activity. The graph shows the z(x) response curve for type 1 (thick line), type 4 (thin line) FFLs, and a simple regulation system (○), for H_zx = H_yx = H_zy = 2. Simulation parameters: α_i = 1, β_i = 1, K_ij = 1, B_i = 0. Type 1 coherent FFL (thick line) has an effective cooperativity of H_eff = H_xz + H_xy*H_yz, where H_ij is the Hill coefficient of the regulation reaction of protein j by protein i. Other coherent FFL types have H_eff = H_zx.