SOLUBLE AND INSOLUBLE TERNARY COMPLEXES OF SERUM-PROTEINS WITH POLYANIONS IN THE PRESENCE OF CU2+ IN WATER

Complex formation between polyacrylic acid (PAA) and bovine serum albu min (BSA), human serum albumin (HSA), hemoglobin (Hb), globin (Gl), an d, respectively, transferrin (Tr), were studied in neutral water. Wate r-soluble and insoluble complexes are formed upon addition of divalent copper ions to the solution. The contacts between proteins and PAA ar e achieved via chelate unit formation in which the copper ions are loc ated at the center. The solubility of the polycomplexes depends on the nature of proteins acid correlates with their isoelectric points (pI) . In the mixtures of Hb-Cu2+-PAA and Gl-Cu2+-PAA, insoluble complexes are formed at pH = pI starting with very low concentrations of Cu2+ (n (Cu)/n(AA) less than or equal to 0.01) On the other hand, these polyco mplexes remain soluble at pH > pi. BSA, HSA, and Tr form soluble terna ry polycomplexes at neutral water (pH 7). The formation of the polycom plexes in the mixture BSA-Cu2+-PAA was intensively studied by titratio n, HPLC, electrophoretic, and spectrophotometric methods. The solubili ty, composition, and stability of these polycomplexes depend on metal/ polymer and protein/polymer ratio. Insoluble polycomplexes are formed when concentration of Cu2+ reaches a critical value (n(Cu)/n(AA) great er than or equal to 0.25). At this concentration of Cu2+, phase separa tion takes place, starting with very low concentration of protein in t he system. Over the critical ratio of the protein/polymer, the mixture again exhibits water-soluble character. The pattern of distribution o f Cu2+ between PAA coils and of protein globules between polymer-metal complex particules appeared to follow the self-assembly principle. A hypothetical structural scheme for the formation of soluble and insolu ble ternary polycomplexes is proposed. (C) 1996 John Wiley & Sons, Inc .