[Complexes of Cu2+ with pyridoxal-5'-phosphate and human and bovine serum albumin].

The copper ion Cu2+ bound to serum albumin in the most strong center stabilizes aldimine bonds formed by PLP with epsilon-NH2 group of 4-Lys and alpha-NH2 1-Asp. The stoichometric ratio of the ternary albumin-PLP-Cu2+ complex is 1:2:1. The imidazole rings of histidine residues are involved in binding of copper ions in the first, second, third centers of the albumin molecule. In this case copper ions increase the binding of PLP with the protein stabilizing Schiff bases produced by epsilon-NH2 group of lysine and PLP. The cooper ion bound to serum albumin in the most strong center forms two types of complexes: with rhombic environment in neutral and alkaline media and axial one at pH less than 5,0. On formation of the ternary complex with PLP the rhombic environment is changed to axial.