| Abstract
| - 15N solid-state NMR (SSNMR) spectra of guanidyl-15N-labeled bacteriorhodopsin (bR) showperturbation of an arginine residue upon deprotonation of the retinal Schiff base during the photocycle.At the ε position, an upfield shift of 4 ppm is observed while the η nitrogens develop a pair of ‘wing'peaks separated by 24 ppm. Proton-driven spin diffusion between the two ‘wing' peaks indicates thatthey arise from a single Arg residue. An unusually asymmetric environment for this residue is indicatedby comparison with guanidyl-15N chemical shifts in a series of arginine model compounds. The ‘wing'peaks are tentatively assigned to Arg-82 on the basis of the SSNMR investigations of the alkaline andneutral dark-adapted forms of the D85N bacteriorhodopsin mutant. Another, less asymmetric pair of ηsignals, that is not affected by Schiff base deprotonation or D85 mutation, is tentatively assigned to Arg-134. The results are discussed in relation to existing models of bR structure and function.
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