Delipidation of bacteriorhodopsin and reconstitution with exogenous phospholipid

Solubilizations of the purple membrane from Halobacterium halobium with the detergent Tritain X-100 followed by gel filtration in deoxycholate solution gave bacteriorhodopsin that was more than 99% free from endogenous lipid. The delipidated bacteriorhodopsin was reconstituted with exogenous phospholipids to form vesicles which on illumination efficiently translocated protons. The direction of proton pumping was from the outside to the interior of the vesicles, indicating that the orientation of bacteriorhodopsin in the vesicles was opposite to that in the bacterial membrane. This orientation was confirmed by cleavage of the carboxyl terminus of the protein by proteolysis from the outside of the vesicles.