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 temperatures. Qualitative changes are observed in the FT-Raman spectrum above the midpoint temperature of the predenaturational transition indicating structural changes and inhomogeneous protein populations. Dark-adapted BR shows an increased all-trans component at 78°C, while light-adapted BR at 78°C is found to contain 13-cis BR, possibly as a result of a reduced extent of light adaptation or a change in protein—chromophore interactions.