SURFACE-CHARGE CONTROL OF ELECTROPERMEABILIZATION AND GLYCOPHORIN ELECTROINSERTION WITH 1,2-DIACYL-SN-GLYCERO-3-PHOSPHOCHOLINE (LECITHIN) LIPOSOMES

Back insertion of a solubilized membrane protein, glycophorin A, has b een obtained in lipid multilamellar Vesicles by applying calibrated el ectric field pulses on a lipid/protein mixture. Experimental evidence for insertion is given by means of immunofluorescence. Insertion was o btained only under field conditions that induced the leakage of a solu ble hydrophilic molecule, calcein, which was trapped between the lipid layers. Studies were performed on mixed liposomes where charged speci es were present. The critical permeabilizing field is the same whateve r the composition, but with overcritical fields the associated calcein transmembraneous flow is higher with positively charged lipids. Field conditions that where prone to trigger glycophorin insertion were sim ilar to those that induced electropermeabilization. No electroinsertio n has been obtained with stearylamine NH(2))/1,2-dipalmitoyl-sn-glycer o-3-phosphocholine (Pam(2)GroPCho) liposomes under the same conditions . Calcein efflux as well as glycophorin insertion are controlled by th e electric surface charge of the host liposome. These observations con firm our previous conclusions that spontaneous membrane protein insert ion is obtained when the host membrane is brought to its electropermea bilized state, but show that a strong control due to the surface charg es is nevertheless present.