Phospholipid monolayers covalently fixed to spherical polymer carriers spontaneously form a stable bilayer-like structure by adsorption of further added phospholipids. Bacteriorhodopsin could be incorporated into the lipid bilayer growing on these particles. From the direction of proton pumping as well as from freeze-fracture electron micrographs and papain digestion, experimental evidence was obtained that the preferred orientation of bacteriorhodopsin within the lipid coat is ‘inside-out’ (more than 90%). A ‘right-side-out’ incorporation of bacteriorhodopsin could be demonstrated, if the negative charge density of the carrier surface was lowered by chemical modification.
