Binding of a chiral drug to a protein: an investigation of the 2-(3-benzoylphenyl) propionic acid/bovine serum albumin system by circular dichroism and fluorescence

A combined approach using global analysis of circular dichroism multiwavelength data and time resolved fluorescence was applied to investigate the interaction of R-(-)- and S-(+)- ketoprofen with bovine serum albumin in buffer solution at neutral pH. A characterization of the most stable drug : protein adducts of 1 : 1 and 2 : 1 stoichiometry, as individual chemical species, was obtained. The stability constants and the absolute circular dichroism spectra of the diastereomeric complexes were determined. The spectra of the 1 : 1 conjugates are opposite in sign, those of the 2 : 1 complexes are both negative, but different in shape from each other ( peaks at 358 and 342 nm for S-( +)- and R-(-)- ketoprofen, respectively). A tryptophan residue was shown to be involved in the binding of the drug, in the primary site for the R-( -) and in the secondary site for the S-( +) enantiomer, thereby showing that chiral recognition by the protein causes the site of highest affinity being not the same for both optical antipodes. RI Monti, Sandra/B-9272-2009; Sortino, Salvatore/E-4684-2011