FIGURE 2.

Fluxes for Biv‐ versus IF binding: implication of the k₃/k₂ ratio. Bivalent‐like, “Biv” refers to IF binding in where the conformational change proceeds faster than the binding, i.e., with k₃ > k₂ compared to k₃ < k₂ for classical IF. It is only from the kinetic viewpoint that such Biv‐ binding behaves similarly as genuine bivalent ligand binding (More information in Supporting Information Section S2). Simulations refer to isolated pathways. From left to right: the binding shifts from a Biv‐ to an IF pattern when the k₃/k₂ ratio decreases. Data for t = 0 not presented. (A) Simulated association/”accumulation” plots of the bound target species (i.e., TL for the intermediate complex and T*L for the final complex) as a function of the incubation time. Microscopic rate constants are provided in Supporting Information Section S3 and comply with the classical frame of reference for each model. [L] = 2.5 × K_D for each example. Please note that [TL] still remains minimal (i.e., <1% of [T_tot]) at all times. It is only at higher [L] that transient rises in [TL] become significant for IF (not shown). (B) Evolution of the microscopic forward fluxes with time. Note that, at equilibrium, F₁ < F₃ for Biv and F₁ > F₃ for IF. (C) Evolution of the macroscopic F_on and F_off with time. Note that at equilibrium, all forward and reverse fluxes cancel out, that F_on is dictated by the smallest microscopic forward flux for Biv and IF and that F_on equals half of the microscopic forward fluxes for the intermediate situation in where F₁ = F₃. (D) The above considerations apply to all [L] at equilibrium