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

The electrophoretic mobilities of liposomes prepared from egg phosphat idylcholine (PC) immersed in solutions which contain amino acids, poly peptides or proteins have been studied. Amino acids (lysine - a basic amino acid, or glutamic acid - an acidic amino acid) cause a pH variat ion which changes the acid-base dissociation equilibria of charged com pounds in the PC membranes. Polypeptides (poly(L-lysine) - a cationic polymer and poly(L-glutamic acid) - an anionic polymer) can adsorb ont o the membrane surface of the PC liposomes because of their high affin ity for the membrane, which causes significant changes in the electrop horetic mobilities towards more positive values in the case of poly(L- lysine) and causes slight negative shifts in the case of poly(L-glutam ic acid). Proteins (serum albumin: isoelectric point, pH 4.9; and cyto chrome c: isoelectric point, pH 10.1) adsorb on the membrane surface, which decreases the negative value of the electrophoretic mobilities i n both cases. Furthermore, both proteins shift the zero point of zeta potential of the lipid liposomes towards the isoelectric point of the proteins.