Reversible Binding of Some Isoxazolyl Penicillins with Serum Albumin using Fluorescence Spectroscopic Technique

Mechanism of interaction of three isoxazolyl penicillins, cloxacillin sodium, dicloxacillin sodium, and flucloxacillin sodium – with bovine serum albumin has been studied using fluorescence spectroscopic technique. The stoichiometry of the interaction was found to be 1:1, and association constants were of the order of 10 in each case. The nature of drug-protein interaction could be predicted from the thermodynamic parameters for the binding. High positive entropy changes and positive enthalpy changes indicated that hydrophobic interactions are predominantly involved in the binding of these drugs to serum albumin. Binding studies carried out in the presence of hydrophobic probe 1-anilinonaphthalene-8-sulfonate (ANS) showed that the drugs and ANS do not share a common site on the albumin molecule. Stern-Volmer analysis of the fluorescence data showed that both the tryptophan residues of albumin are involved; but they are not fully accessible to the drugs, and static quenching mechanism is operative.