Binding of sulindac to human serum albumin studied by circular dichroism

The protein binding of sulindac (CAS 38194-50-2) was studied using circular dichroism (CD). By the new algorithm for the analysis of proposed data the association constants (k) and number of binding sites (N) were determined. The binding was found to go through separate stages, where the binding affinity tends to become lower; the first step characterized by kI = 7.6 x 10(6) l.mol-1 and NI = 1.4; while for the second step kII = 1.7 x 10(6) l.mol-1 and NII = 6.6. On the basis of the CD-data and using UV-spectra the nature of binding sites was studied. It may be stated that the binding sites are situated in the region of asymmetrically perturbed chromophore of the drug, which made a positive contribution to the Cotton effect. The results obtained suggest a mechanism of interaction which is consistent with the stepwise binding model.