THE ORIGIN OF THE RED-SHIFTED ABSORPTION MAXIMUM OF THE M412 INTERMEDIATE IN THE BACTERIORHODOPSIN PHOTOCYCLE |
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Authors: | Y. Gat M. Sheves |
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Affiliation: | Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel |
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Abstract: | The factors that red shift the absorption maximum of the retinal Schiff base chromophore in the M412 intermediate of bacteriorhodopsin photocycle relative to absorption in solution were investigated using a series of artificial pigments and studies of model compounds in solution. The artificial pigments derived from retinal analogs that perturb chromophore-protein interactions in the vicinity of the ring moiety indicate that a considerable part of the red shift may originate from interactions in the vicinity of the Schiff base linkage. Studies with model compounds revealed that hydrogen bonding to the Schiff base moiety can significantly red shift the absorption maximum. Furthermore, it was demonstrated that although s-trans ring-chain planarity prevails in the M412 intermediate it does not contribute significantly (only ca 750 cm−1) to the opsin shift observed in M412. It is suggested that in M412, the Schiff base linkage is hydrogen bonded to bound water and/or protein residues inducing a considerable red shift in the absorption maximum of the retinal chromophore. |
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