The investigation of interaction of polyacrylic acid with bovine serum albumin by dynamic and electrophoretic light scattering methods

Water-soluble and insoluble protein-polyelectrolyte complexes as a functional biopolymersystems represent a specific class of polymer-protein compounds that have been the subject ofmany studies such as protein purification, enzyme immobilization and development ofsynthetic vaccines. Electrostatic interactions are the main forces in PPC formations; however,hydrophobic effects and hydrogen bondings are also possible. The interactions ofpolyelectrolytes (PE) with proteins in aqueous solutions is found to be pH, ionic strength andprotein/polyelectrolyte ratio dependent.In this study, the interactions between bovine serum albumin (BSA) as a globular protein andpoly(acrylic acid) (PAA) as a weak polyelectrolyte were investigated by using dynamic andelectrophoretic light scattering techniques. BSA-PAA systems were analyzed at different pHvalues and protein/polymer ratios. Dynamic light scattering results show that there was nocomplex formation at pH 7.0 and water-soluble complexes was formed at pH 5.0. Water-insoluble complexes formed in the mixtures of BSA-PAA prepared at pH 4.0 and it wasshown that free BSA molecules coexist with water-soluble polycomplexes, which are largerthen components, in the supernatants after centrifugation. According to the electrophoreticlight scattering measurements, complex molecules were always negatively charged at pH 5.0,but at pH 4.0 complex particles were positively charged after a certain ratio of components.