Structural Changes in the Retinal Chromophore of Bacteriorhodopsin Studied by Resonance Raman Spectroscopy

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Abstract
Resonance Raman (RR) spectra were obtained from aqueous suspensions of the purple membrane of Halobacteria. The RR spectra reflect the photolabile retinal chromophore of bacteriorhodopsin which induces proton translocation across the membrane. RR spectra of the all‐trans chromophore BR570 and its 13‐cis component BR548 were recorded both in H2O and D2O suspension. The vibrational analysis revealed characteristic hydrogen bending modes of the Schiff base linkage by which retinal is bound to the protein. These bands are very sensitive to structural changes of the Schiff base and allow conclusions on geometrical and electronic changes of this group which play an important role in the proton translocation process.