Analysis of binding interaction of curcumin and diacetylcurcumin with human and bovine serum albumin using fluorescence and circular dichroism spectroscopy.

The current study reports the binding of curcumin (CUR) as the main pharmacologically active ingredient of turmeric and diacetylcurcumin (DAC) as a bioactive derivative of curcumin to human serum albumin (HSA) and bovine serum albumin (BSA). The apparent binding constants and number of substantive binding sites have been evaluated by fluorescence quenching method. The distance (r) between donor (HSA and BSA) and acceptor (CUR and DAC) was obtained on the basis of the Förster's theory of non-radiative energy transfer. The minor changes on the far-UV circular dichroism spectra resulted in partial changes in the calculated secondary structure contents of HSA and BSA. The negligible alteration in the secondary structure of both albumin proteins indicated that ligand-induced conformational changes are localized to the binding site and do not involve considerable changes in protein folding. The visible CD spectra indicated that the optical activity observed during the ligand binding due to induced-protein chirality. All of the achieved results suggested the important role of the phenolic OH group of CUR in the binding process.