Electrostatic interactions between charges on ligands and charges on proteins that are remote from the binding interface can influence the free energy of binding (Δ G b ). The binding affinities between charged ligands and the members of a charge ladder of bovine carbonic anhydrase (CAII) constructed by random acetylation of the amino groups on its surface were measured by affinity capillary electrophoresis (ACE). The values of Δ G b derived from this analysis correlated approximately linearly with the charge. Opposite charges on the ligand and the members of the charge ladder of CAII were stabilizing; like charges were destabilizing. The combination of ACE and protein charge ladders provides a tool for quantitatively examining the contributions of electrostatics to free energies of molecular recognition in biology.
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