Molecular complexation of uracil with bovine serum albumin and its complex with bilirubin studied by spectroscopic methods

The interactions of uracil (U) with bovine serum albumin (BSA) and its complex with bilirubin (BR·BSA) in phosphate buffer at pH 7.4 were studied by fluorescence and electronic spectroscopy. The parameters of the resulting intermolecular complexes (binding constants, quenching rate constants, the radius of the quenching sphere-of-action, etc. ) were determined. The interaction of BSA with U occurs through a static quenching of protein fluorescence and has a predominantly hydrophobic character. The effect of U on the conformational changes of the protein molecule was analyzed by synchronous fluorescence spectroscopy. Uracil binds to BR·BSA more efficiently than to the free protein due to the interaction of U with the tetrapyrrole pigment incorporated in the macromolecular complex.