The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) have been studied by fluorescence and circular dichroism spectroscopy. The binding of 3-carboxyphenoxathiin quenches the BSA and HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 105 M-1. In addition, according to the synchronous fluorescence spectra of BSA and HSA in presence of 3-carboxyphenoxathiin, the tryptophan residues of the proteins are most perturbed by the binding process. Finally, the distance between the acceptor, 3-carboxyphenoxathiin, and the donor, BSA or HSA, was estimated on the basis of the Förster resonance energy transfer (FRET). The fluorescence results are correlated with those obtained from the circular dichroism spectra, which reveal the change of the albumin conformation during the interaction process.

The binding of ofloxacin (OFLX) to human serum albumin (HSA) was investigated by fluorescence and circular dichroism (CD) techniques. The binding parameters have been evaluated by a fluorescence quenching method. Competitive binding measurements were performed in the presence of warfarin and ibuprofen and suggest binding to the warfarin site I of HSA. The distance r between donor (HSA) and acceptor (OFLX) was estimated according to the Forster's theory of non-radiatiative energy transfer. CD spectra revealed that the binding of OFLX to HSA induced conformational changes in HSA. Molecular docking was performed and shows that for the lowest energy complex OFLX is located in site I of HSA, which correlate to the competitive binding experiments.

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Abstract:© Versita Sp. z o.o. Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4.Quenching constants were determined using the Lineweaver-Burk equation to provide a measure of the binding affinity of coumarin-3-carboxylic acid to HSA/BSA. Binding studies concerning the number of binding sites, n, and apparent binding constant, K, were performed by a fluorescence quenching method at different temperatures (298, 303 and 310 K). The thermodynamic parameters, enthalpy change (ΔH 0 ) and entropy change (ΔS 0 ) as calculated according to the van't Hoff equation, indicated that hydrogen bonding and van der Waals forces play a major role in coumarin-3-carboxylic acid-HSA association whereas electrostatic interactions dominate in coumarin-3-carboxylic acid-BSA association. The distance, r, between the donor (HSA/BSA) and acceptor (coumarin-3-carboxylic acid) has been estimated using Förster's equation, on the basis of resonance energy transfer. Furthermore, CD spectra were used to investigate the α-helix changes of the HSA and BSA molecules upon addition of coumarin-3-carboxylic acid.