ENERGY-TRANSDUCING PROPERTIES OF PRIMARY PROTON PUMPS RECONSTITUTED INTO ARCHAEAL BIPOLAR LIPID VESICLES

Archaeal lipids differ considerably from eubacterial and eukaryotic li pids in their structure and physical properties. From the membranes of the extreme thermophilic archaea Sulfolobus acidocaldarius a tetraeth er lipid fraction was isolated, which can form closed and stable monol ayer liposomes in aqueous media. The function of three different prima ry proton pumps originating from archaeal, bacterial and eukaryotic li pid sources have been studied after reconstitution in these liposomes: bacteriorhodopsin from the archaea Halobacterium halobium; cytochrome -c oxidase from the thermophilic bacterium Bacillus stearothermophilus and cytochrome-c oxidase from beef heart mitochondria. Liposomes comp osed of tetraether lipids form a competent matrix for all three exogen ous proton pumps. Bacteriorhodopsin was inserted inside-out in these l iposomes, as normally observed in bilayer-forming lipid. The activitie s of the two oxidases were inhibited at high tetraether-lipid concentr ation, probably due to the low fluidity of these membranes. Only bacte riorhodopsin, which originates from diether archaeal lipids is fully f unctional in the tetraether membranes.