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

<p>(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 <i>k</i>_<i>r</i>, and is excited from the ground state with rate <i>k</i>_<i>e</i>. (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 <i>k</i>_<i>e</i>, and relaxes back into the ground state with rate <i>k</i>_<i>r</i>. (c) The dominant, smallest relaxation rate <i>k</i>_obs of induced-fit binding is minimal at the total ligand concentration where [P]₀ is the total protein concentration and <i>K</i>_<i>d</i> the overall dissociation constant. As a function of [L]₀, the dominant rate <i>k</i>_obs is symmetric with respect to this minimum. (d) The dominant, smallest relaxation rate <i>k</i>_obs of conformational-selection binding has a characteristic minimum as a function of [L]₀ for <i>k</i>_<i>e</i> > <i>k</i>₋, but is not symmetric with respect to this minimum. (e) The dominant rate <i>k</i>_obs of conformational-selection binding decreases monotonically with [L]₀ for <i>k</i>_<i>e</i> < <i>k</i>₋.