Figure 4. Multisite phosphorylation in a double-negative feedback loop.

Top: we assume that X is inactivated by phosphorylation and the active forms of X promote the degradation of the protein kinase, K. For fixed values of K, the steady state activity of X (the solid line) is given by Eq. (3) in the ordered case (A) and Eq. (5) in the disordered case (B). For fixed values of X_a, the steady value of K (the dashed line) is given by Eq. (9). Parameter values: κ_s = 0.02, κ_d = 0.02, κ_a = 0.98, X_T = 1, N = 10, q = 0, h = 0.1 (ordered) or 0.5 (disordered).