Spectroscopic investigation on the interaction of a cyarline dye with serum albumins

The interactions of a cyanine dye with human serum albumin (HSA) and bovine serum albumin (BSA) have been investigated by using absorption and fluorescence spectra. Absorption spectral studies show that binding to the serum albumins leads to a bathochromic shift of the monomer band together with a notable intensity change. Furthermore, the number of binding sites (n) was identified by the absorption spectra. There is a constant enhancement of fluorescence quantum yield when the cyanine dye complexes with HSA or BSA. The apparent binding constant (K(a)) and the free energy changes (Delta G) were obtained by analysis of fluorescence data of the cyanine dye in the absence and presence of HSA and BSA. Compared to BSA, HSA associates with the dye in a stronger way.