Comparative Investigation of the Spectral Characteristics of Complexes of Hoechst 33258 and Methylene Blue with Bovine Serum Albumin

A comparative investigation of the reaction of the bisbenzimidazole compound Hoechst 33258 and the thiazine dye methylene blue (MB) with bovine serum albumin (BSA) was carried out by spectroscopic methods. Denaturation curves and absorption and differential absorption spectra of the protein-ligand complexes were obtained. It was shown that the denaturation temperature of the albumin complexes of BSA with Hoechst 33258 decreases with increase of the ligand/protein concentration ratio whereas in the case of MB the denaturation temperature increases. Changes in the absorption spectra and differential absorption spectra of the complexes of the ligands with albumin resulting from combination of these specific ligands with the protein were observed. It is supposed that during interaction of Hoechst 33258 with BSA some loosening of the protein compact structure occurs as a result of partial loss of helicity in the alpha structures, whereas in the case of MB the degree of packing in the spatial structure of the protein is increased.