Interaction of curcumin and diacetylcurcumin with the lipocalin member beta-lactoglobulin.

The binding of curcumin (CUR) and diacetylcurcumin (DAC) to bovine beta-lactoglobulin (BLG) genetic variant B was investigated by fluorescence and circular dichroism techniques. The binding parameters including number of substantive binding sites and the binding constants have been evaluated by fluorescence quenching method. The distance (r) between donor (BLG) and acceptor (CUR and DAC) was obtained according to the Förster's theory of non-radiative energy transfer. The far-UV circular dichroism spectra were used to investigate the possible changes in the secondary structure of BLG in the presence of CUR and DAC and showed that these two ligands change the alpha-helix and random coil contents of this protein to some extent. The visible circular dichroism spectra indicated that the optical activity during the ligand binding was observed due to the induced-protein chirality. All of the achieved results suggested the important role of the phenolic OH group of CUR in the binding process resulted in more affinity of CUR than DAC for binding to BLG.