Serum albumin and its bilirubin complex as drug-carrier proteins for water-soluble porphyrin: a spectroscopic study

The interactions of bovine serum albumin (BSA) and its bilirubin (BR) macromolecular complex (BR center dot BSA) with meso-tetrakis-(p-sulfophenyl)porphin (TSPP) have been studied by electronic spectroscopy, and emission and synchronous fluorescence in phosphate buffer at pH 7.4. The parameters of the resulting intermolecular complexes (binding constants, quenching rate constants, etc.) were established. The values of the binding constants for the BSA-TSPP and BR center dot BSA-TSPP systems were 13 x 10(4) and 8.0 x 10(4) dm(3) mol(-1), respectively. The interaction of TSPP with the proteins is studied by static quenching of protein fluorescence, showing predominantly hydrophobic and electrostatic nature. During the complex-formation process, a bathochromic shift of the TSPP Soret band occurs. The influence of TSPP on conformational changes of the protein molecules was analyzed using synchronous fluorescence spectroscopy. It was found that there is competition of BR with TSPP for binding sites on the protein, resulting in displacement of BR from the complex. .