Fig 1. Characteristic chemical relaxation of induced-fit and conformational-selection binding.

(a) In induced-fit binding, the change between the conformations P₁ and P₂ of the protein occurs after binding of the ligand L. The intermediate state P₁L relaxes into the bound ground state P₂L with rate k_r, and is excited from the ground state with rate k_e. (b) In conformational-selection binding, the conformational change of the protein occurs prior to ligand binding. The intermediate state P₂ is excited from the unbound ground state P₁ with rate k_e, and relaxes back into the ground state with rate k_r. (c) The dominant, smallest relaxation rate k_obs of induced-fit binding is minimal at the total ligand concentration ${\left[\text{L}\right]}_0^{\text{min}}={\left[\text{P}\right]}_0-K_d$ where [P]₀ is the total protein concentration and K_d the overall dissociation constant. As a function of [L]₀, the dominant rate k_obs is symmetric with respect to this minimum. (d) The dominant, smallest relaxation rate k_obs of conformational-selection binding has a characteristic minimum as a function of [L]₀ for k_e > k₋, but is not symmetric with respect to this minimum. (e) The dominant rate k_obs of conformational-selection binding decreases monotonically with [L]₀ for k_e < k₋.