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. 2007 May 25;93(7):2279–2288. doi: 10.1529/biophysj.107.109132

FIGURE 2.

FIGURE 2

Bistability due to Mek sequestration. (A) Bistable stimulus response of the core MAPK cascade. Extracellular stimulation was simulated by varying the total concentration of active Raf (pRaftot = pRaf + pRaf-Mek + pRaf-pMek), and bisphosphorylated Erk (ppErk) was taken as the response. The black curve corresponds to the previously analyzed basic model (Fig. 1 D, black arrows), whereas the gray stimulus-response was obtained for the sequestration model, which additionally takes Mek sequestration by Erk into account (Fig. 1 D, black and gray arrows). Kinetic parameters are given in Table 1. (B) Mek release from inactive sequestration complexes upon cascade activation. The amount of sequestered Mek (i.e., Mek-Erk + Mek-pErk + pMek-Erk + pMek-pErk) and the total amount of bisphosphorylated Mek (i.e., ppMek + ppMek-Erk + ppMek-pErk) is shown as a function of total active Raf for the kinetic parameters given in Table 1.