FIGURE 6.

Reducing GAP-accelerated conversion of Ras-GTP to Ras-GDP enhances PI3K recruitment but not in proportion to the overall increase in Ras-GTP. The influence of the Ras-GTP lifetime, τ_GAP, on receptor-mediated PI3K recruitment was assessed. Other relevant parameters were set to their base-case values (Table 1), and N_Ras = 1000. (a) Fraction of receptor/PI3K associations mediated by Ras, M_P. (b) Dimensionless rate of Ras activation, α_GEF. (c) Frequencies of Loops II and IIIA as depicted in Fig. 1 c. Asterisk symbols indicate the frequency of Loop IIIB multiplied by the ratio τ_SP/τ_RP = 0.01. (d) Coincidence ratio for simultaneous GEF and PI3K binding to the receptor, C_EP.