Figure 9.

Integrative model shows counteracting effects of rate enhancement and rate reduction. Rate reduction from ZAP70 binding (λ_Z < 1 indicated by color) abrogates the switch-like dose response conferred by rate enhancement of kinase phosphorylating TCR λ_K = 1.2 for both amount of phosphorylation (A) and amount of ZAP70 bound (B), in addition to reducing the saturating value (E_max) of ZAP70 binding (B). (C) Ultrasensitivity quantified using the log-effective-concentration definition of Hill coefficient (Eq. S2) is shown for a range of λ_K ≥ 1 and λ_Z ≤ 1. To see this figure in color, go online.