PARTIAL DELIPIDATION OF PURPLE MEMBRANES BY TWEEN-20 - CHANGES IN SURFACE ELECTRIC PROPERTIES

The charge asymmetry, electric polarizability and electrokinetic charg e of native and lipid-depleted purple membrane fragments were determin ed by means of electric light scattering and Doppler-electrophoretic l ight scattering. Successive stages of lipid depletion produce a sharp drop, followed by an increase and then a gradual decrease in the perma nent dipole moment. The observed effects are interpreted in terms of r emoval of lipids alternately from the inner and outer leaflets of the membrane bilayer. The variations of the electric moments with the decr ease in lipid content occur in parallel with the three phases of delip idation shown to have distinct effects on the photocycle dynamics [Fuk uda et al., Biochemistry, 29 (1990) 1997].