EFFECT OF AMINO-ACIDS, POLYPEPTIDES AND PROTEINS ON ELECTROPHORETIC MOBILITIES OF PHOSPHOLIPID LIPOSOMES

The electrophoretic mobilities of liposomes prepared from egg phosphatidylcholine (PC) immersed in solutions which contain amino acids, polypeptides or proteins have been studied. Amino acids (lysine - a basic amino acid, or glutamic acid - an acidic amino acid) cause a pH variation which changes the acid-base dissociation equilibria of charged compounds in the PC membranes. Polypeptides (poly(L-lysine) - a cationic polymer and poly(L-glutamic acid) - an anionic polymer) can adsorb onto the membrane surface of the PC liposomes because of their high affinity for the membrane, which causes significant changes in the electrophoretic mobilities towards more positive values in the case of poly(L-lysine) and causes slight negative shifts in the case of poly(L-glutamic acid). Proteins (serum albumin: isoelectric point, pH 4.9; and cytochrome c: isoelectric point, pH 10.1) adsorb on the membrane surface, which decreases the negative value of the electrophoretic mobilities in both cases. Furthermore, both proteins shift the zero point of zeta potential of the lipid liposomes towards the isoelectric point of the proteins.