The purple membrane isolated from Halobacterium halobium contains only a single protein, bacteriorhodopsin, which functions as a light-driven proton pump. Substantial structural information has been obtained which has led to specific models of protein structure in the membrane (Engelman et al., 1982; Huang et al., 1982; Agard & Stroud, 1982). The retinal chromophore of bacteriorhodopsin is boun...
