Protein-Polyelectrolyte Complexes

Abstract

Proteins interact strongly with both synthetic and natural polyelectrolytes. Ample evidence exists for the binding of polyanions and polycations to proteins below and above their isoelectric points, respectively. These interactions may result in soluble complexes [1,2], complex coacervation [3–6], or the formation of amorphous precipitates [7–9]. The practical consequences of these phase changes may include the use of polyelectrolytes for protein separation [10–16] and immobilization or stabilization of enzymes in polyelectrolyte complexes [17–18]. In these two applications, the optimal physical states of the system are different. In the case of enzyme immobilization, highly deaggregated states may be less active. In purification or separation processes involving settling or filtration, aggregation is desirable. For efficient settling, close-packed aggregates are preferred, whereas in filtration processes more open-textured aggregates are needed to allow adequate solvent penetration. However, in both cases the aggregation should be essentially reversible.