Electrophoretic and quasi-elastic light scattering of soluble protein-polyelectrolyte complexes

Abstract

Complexation between globular proteins (bovine serum albumin, bovine pancreas ribonuclease, and chicken egg lysozyme) and a number of synthetic polyelectrolytes was studied by quasi-elastic light scattering (QELS) and electrophoretic light scattering in dilute electrolyte solution. For each polyion-protein pair, there is a well-defined critical pH at which binding commences (pH,). At this pH, QELS reveals fast and slow diffusion modes corresponding to free protein and complex, respectively; the relative amplitude of the latter increases with pH in the case of polycations, with opposite pH dependence for polyanions. Further pH change produces phase separation at a second well-defined point (pH+). The electrophoretic mobility of the polymer begins to change at pH, and moves toward zero as pH approaches pH+. These results are discussed in terms of (1) the role of protein “charge patches” as binding sites and (2) the alternative possibilities of intra- and inter-polyion