The binding of propranolol (PROP) to human serum albumin (HSA) in the absence and presence of quercetin (QUER) in aqueous solution was investigated by multiple techniques. The presence of quercetin (QUER) increased binding constant of propranolol (PROP) with HSA. Fluorescence spectroscopy showed that quercetin (QUER) could quench the HSA fluorescence spectra. The results of synchronous fluorescence, resonance light scattering (RLS) and three-dimensional fluorescence spectra showed that propranolol (PROP) and quercetin (QUER) would alter the microenvironment around tryptophan (Trp) and tyrosine (Tyr) residues. According molecular dynamics (MD) simulation results suggested that these ligands can interact with the protein, with affecting the secondary structure of HSA and with a modification of its tertiary structure. Molecular docking studies showed that the affinity and binding site of each of the ligands to HSA altered in the presence of the other. All above results may have related consequence in rationalizing the interferences of ordinary food to cardiac dysrhythmias treatments

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