[Study of the interaction of pyridoxal-5'-phosphate and human serum albumin in the presence of copper ions by circular dichroism].

When pyridoxal-5'-phosphate (PLP) binds with human serum albumin (HSA) in the molar ratio of 1:1, negative in sign induced Cotton effect is observed in the ligand absorption band. This high affinity center is localized in the second domain at an alpha-helical site of the protein molecule. As a result of adding Cu2+ equimolar concentration a new optically active PLP binding site with the positive sign of Cotton effect is acidic medium and the opposite one in alkaline medium is formed on Lys-4 at the beginning of the polypeptide chain. Inversion of the CD spectrum occurs over the same range of pH of the medium as the change in symmetry of electric field surroundings (rhombic in equilibrium axial) of the copper ion within the equimolar ternary complex HSA: PLP: Cu2+.