Binding of ketoprofen to human serum albumin studied by circular dichroism.

The protein binding of ketoprofen has been studied using circular dichroism titration method as well as the new algorithm proposed by the authors for the treatment of data obtained. The quantitative parameters association constants (k) and number of binding sites (N) have been determined. It is proved that the protein binding of Ketoprofen is going through separate stages and the number of binding sites probably arises. It is acceptable that a high affinity binding takes place primarily (kI = 3.8 x 10(6) l.mol-1). Later, due to the conformational changes in the protein molecule the binding areas are modified and the number of binding sites considerably arises (NI = 3.5 and NII = 14), while the binding affinity reduces 100-fold (kII = 5.10(4) l.mol-1). The number of binding sites has been studied and an identification of the chromophore taking part in the drug-protein interaction has been performed on the base of UV- and CD spectra. A mechanism of the interaction is proposed which coincides with the stepwise binding model.