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  • Title: Low-temperature solid-state 13C NMR studies of the retinal chromophore in rhodopsin.
    Author: Smith SO, Palings I, Copié V, Raleigh DP, Courtin J, Pardoen JA, Lugtenburg J, Mathies RA, Griffin RG.
    Journal: Biochemistry; 1987 Mar 24; 26(6):1606-11. PubMed ID: 3593680.
    Abstract:
    Magic angle sample spinning (MASS) 13C NMR spectra have been obtained of bovine rhodopsin regenerated with retinal prosthetic groups isotopically enriched with 13C at C-5 and C-14. In order to observe the 13C retinal chromophore resonances, it was necessary to employ low temperatures (-15-----35 degrees C) to restrict rotational diffusion of the protein. The isotropic chemical shift and principal values of the chemical shift tensor of the 13C-5 label indicate that the retinal chromophore is in the twisted 6-s-cis conformation in rhodopsin, in contrast to the planar 6-s-trans conformation found in bacteriorhodopsin. The 13C-14 isotropic shift and shift tensor principal values show that the Schiff base C = N bond is anti. Furthermore, the 13C-14 chemical shift (121.2 ppm) is within the range of values (120-123 ppm) exhibited by protonated (C = N anti) Schiff base model compounds, indicating that the C = N linkage is protonated. Our results are discussed with regard to the mechanism of wavelength regulation in rhodopsin.
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