title: Asymmetric structure of the purple membrane.
abstract: There is both functional and structural evidence that bacteriorhodopsin is oriented asymmetrically across the purple membrane of Halobacterium halobium. To assess the degree of asymmetry, the x-ray diffraction data from the membrane have been analyzed for possible electron-density profiles. A recent theory predicts that only a limited number of profiles are consistent with the continuous diffraction data, and two possible profiles have been found. Both profiles indicate that the protein molecules span a lipid bilayer in the membrane. Both profiles are asymmetric; there are more lipid molecules in one half of the membrane than in the other, and the bacteriorhodopsin molecule shows a slight complementary asymmetry.
mesh_terms: D001436:Bacteriorhodopsins; D002338:Carotenoids; D002462:Cell Membrane / Q000648:ultrastructure; D005583:Fourier Analysis; D006217:Halobacterium / Q000648:ultrastructure*; D008563:Membrane Lipids; D014961:X-Ray Diffraction
chemical_list: D008563:Membrane Lipids; D002338:Carotenoids; D001436:Bacteriorhodopsins