Interaction of a cationic polymer with negatively charged proteoliposomes

Proteoliposomes were prepared by making bilayer vesicles from neutral egg y olk lecithin and negatively charged alpha -chymotrypsin that had been previ ously stearoylated. Interaction of these proteoliposomes with a cationic po lymer, poly-(N-ethyl-4-vinylpryidinium bromide) (PEVP) was examined. For co mparison purposes, interaction of PEVP with egg lecithin vesicles containin g an anionic phospholipid, cardiolipin, was also examined. Binding of PEVP to both types of vesicles was electrostatic in nature with the polymer mani festing a higher affinity to the cardiolipin relative to the enzyme. PEVP h ad no effect on the permeability of the bilayer membranes to sodium chlorid e. On the other hand, PEVP increased the transmembrane permeability of the nonionic anti-tumor drug, doxorubicin. The greater the negatively charged c omponent in the membrane, the greater the PEVP effect. Polycation binding t o the vesicles was accompanied by clustering of the stearoylated chymotryps in (sCT) molecules within the membrane. This protein clustering is most lik ely responsible for the increase in the doxorubicin permeation. Enzymatic a ctivity of the membrane-associated sCT remained unchanged upon PEVP binding . These findings seem relevant to the effects of polyelectrolytes on cellul ar membranes. (C) 2001 Published by Elsevier Science B.V.