A FOURIER-TRANSFORM RAMAN-STUDY OF THE TEMPERATURE-DEPENDENCE OF CHROMOPHORE CONFORMATION IN LIGHT-ADAPTED AND DARK-ADAPTED BACTERIORHODOPSIN

Fourier-transform Raman spectra are reported for bacteriorhodopsin (BR ) in its light-adapted and dark-adapted states at room and elevated te mperatures. Qualitative changes are observed in the FT-Raman spectrum above the midpoint temperature of the predenaturational transition ind icating structural changes and inhomogeneous protein populations. Dark -adapted BR shows an increased all-trans component at 78-degrees-C, wh ile light-adapted BR at 78-degrees-C is found to contain 13-cis BR, po ssibly as a result of a reduced extent of light adaptation or a change in protein-chromophore interactions.