Figure 5.
Ultrasensitivity. (a) R, total K, P and KP are numerically calculated as KPB is changed in the extended model with only kinase active (Figure 2d). Parameters used are: λ−1 = 10 s−1,λ1 = 1μM−1s−1,k1 = 100 s−1,λ−2 = 10 s−1,λ2 = 1μM−1s−1,k2 = 100 s−1,λ−4 = 10 s−1,λ4 = 100μM−1s−1,k4 = 0.01 s−1,κ−1 = 10 s−1,κ1 = 1μM−1s−1,Pt = 10μM,St = 1μM.Hill coefficient for basic model and active K is nH = 1 and nH = 1.8, respectively. (b) R, total K, P and KP are numerically calculated as KPB is changed in the extended model with only phosphatase active (Figure 2c). Parameters used are: λ−1 = 10 s−1,λ1 = 1μM−1s−1,k1 = 100 s−1,λ−2 = 10 s−1,λ2 = 1μM−1s−1,k2 = 100 s−1,λ−3 = 10 s−1,λ3 = 100μM−1s−1,k3 = 0.01 s−1,κ−1 = 10 s−1,κ1 = 1μM−1s−1,Pt = 10μM,St = 1μM. Hill coefficient for basic model and active K is nH = 1 and nH = 1.95, respectively. In both case the bottom panels show that the level of enzymes remains above the substrate, so we are far from the zero-order regime.