Transient Resonance Raman Spectra of Bacteriorhodopsin and Halorhodopsin
Bacteriorhodopsin (bR) and halorhodopsin (hR) are light-dependent electrogenic proteins in the membrane of Halobacterium halobium (see Ref. 1 for a review). For both proteins, the species which have all-trans retinal chromophore linked to ε-nitrogen of lysine through a protonated Schiff base undergo the cis-trans isomerization to the 13-cis form upon illumination with light. The photo-isomerization of the chromophore is followed by a structural change of a protein moiety to compensate for the energy increase due to the charge separation between the protonated Schiff base and its counter anion. In the mechanism of the structural change a difference appears between the two proteins: unidirectional proton and chloride translocation through the membrane for bR and hR, respectively. In the case of bR, the Schiff base proton is transferred to the protein moiety upon the change from the L to M intermediates, which occurs on a µs time scale, but the photoreaction of hR is not accompanied by deprotonation of the Schiff base. It is interesting to study the structural details of the transient species of these two proteins on a µs time scale.
KeywordsSchiff Base Probe Beam Pump Beam Difference Spectrum Raman Line
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