Static and Dynamic Aspects of Supramolecular Interactions of Coumarin 153 and Fluorescein with Bovine Serum Albumin

Abstract

The static and dynamic aspects of supramolecular interactions between coumarin 153 (C153) and fluorescein (FL) with bovine serum albumin (BSA) has been studied by spectroscopic techniques. Both dyes were found to form 1 : 1 complexes with BSA, with binding constants 2.9 ± 0.3 × 105 M–1 and 2.1 ± 0.2 × 105 M–1 for C153 and FL respectively. The binding site of C153 has been determined by steady-state fluorescence resonance energy transfer, site marker competitive experiments, and a molecular docking study. Our studies indicate that C153 binds to domain IIIA of BSA whereas FL binds non-specifically. Denaturation characteristics of the C153 and FL binding region of BSA were found to be very different to global denaturation. Furthermore, kinetics of binding has been studied by the stopped-flow method. The observed rate constants were found to be 8.8 s–1 and 5.9 s–1 for C153 and FL respectively.