A study of the interaction between fluorescein sodium salt and bovine serum

Abstract

The binding of fluorescein sodium salt with three kinds of commercially available bovine serum albumin
(BSA) of different grades of purity was investigated at 288, 298 and 313 K by fluorescence and absorption
measurements at pH 7.50. The association and dissociation constants Ka and Kd were determined by the
quenching of BSA fluorescence in the presence of fluorescein sodium salt. The best results were obtained
by fitting raw data by non-linear regression and Lineweaver–Burk equations. The modified Stern–Volmer
and Scatchard plots gave less reliable data since the fitting was much more difficult.
The agreement of the constants for the three sets of measurements coming from the different BSA was
not as good as expected. BSA binding properties differ depending on the different BSA grades of purity.
Actually, the binding constants found for the three BSAs used differed in the same set of interactions,
even by keeping the experimental conditions constant. These results are a novelty in the field of
BSA–ligand binding studies and should be taken into account for future binding studies using BSA.
Actually, a large number of aspects should be considered including the grade of purity and the presence
of BSA covalent and non-covalent dimers, trimers and oligomers in solution which can affect the
goodness of the binding results.