CAPILLARY-ELECTROPHORESIS AND DYNAMIC LIGHT-SCATTERING-STUDIES OF STRUCTURE AND BINDING CHARACTERISTICS OF PROTEIN-POLYELECTROLYTE COMPLEXES

Complex formation between sodium polystyrenesulfonate (NaPSS) and two proteins, bovine serum albumin and beta-lactoglobulin, was studied by dynamic light scattering (DLS) and capillary electrophoresis (CE) over a range of polyelectrolyte molecular weights. We found that the dimen sions of the polyelectrolyte chain do not appear to change significant ly upon complex formation and that the dependence of complex mobility on its composition is in agreement with a free-draining model. Estimat es of intrinsic binding constants, sizes of binding site, and cooperat ivities in complex formation were obtained by fitting experimental dat a to the ''overlapping binding sites'' model. It was found that the co operativities shown by the binding isotherms are consistent with the d ependence of binding density upon NaPSS molecular weights. The latter can be predicted by the overlapping binding sites model for known bind ing cooperativity, but was not observed experimentally before.