RESONANCE RAMAN SPECTRA OF THE “BLUE” and THE REGENERATED “PURPLE” MEMBRANES OF Halobacterium halobium

Abstract— We have obtained the resonance Raman spectra of the deionized form of the purple membrane, the so called blue membrane, as well as the purple membrane regenerated by titrating the blue membrane with either Na+, Ca²+ or La³+. All types of regenerated purple membrane have identical Raman spectra which are virtually indistinguishable from the native light‐adapted bacteriorhodopsin spectrum. On the other hand, Raman data for the blue membrane suggest that it consists of essentially two pigment forms with absorption maxima around 605 and 570 nm and containing 13‐cis and all‐trans isomeric configurations of the chromophore. This is consistent with our chromophore extraction results which reveal that the blue membrane consists of 30% 13‐cir and 70%all‐trans chromophore.