The characterization of two specific drug binding sites on human serum albumin

The binding of a number of fluorescent probe molecules to human serum albumin (HSA) has been studied. Small changes in the amino acid moiety of the dansylamino acids resulted in large changes in the binding of these compounds of HSA. It is suggested that electrostatic and dipolar forces play a role in the specificity and binding affinity of such compounds. Fluorescent probes which had one tight binding site were used for drug displacement studies. Changes in probe fluorescence were shown, by equilibrium dialysis and by fluorescence titrations, to be a result of competitive displacement by drugs. The pattern of displacement of probes by drugs enabled the identification of two specific drug binding sites. The relative affinity of drugs for these binding sites was measured by their ability to displace fluorescent probes specific for the sites. The method provides a rapid and simple means for detecting potential drug interactions based on competition for protein binding sites.