Smith S O, Palings I, Copié V, Raleigh D P, Courtin J, Pardoen J A, Lugtenburg J, Mathies R A, Griffin R G
Biochemistry. 1987 Mar 24;26(6):1606-11. doi: 10.1021/bi00380a018.
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.
已获得用在C-5和C-14处同位素富集13C的视网膜辅基再生的牛视紫红质的魔角样品旋转（MASS）13C NMR光谱。为了观察13C视网膜发色团共振，有必要采用低温（-15至-35摄氏度）来限制蛋白质的旋转扩散。13C-5标记的各向同性化学位移和化学位移张量的主值表明，视紫红质中的视网膜发色团处于扭曲的6-s-顺式构象，这与细菌视紫红质中发现的平面6-s-反式构象形成对比。13C-14各向同性位移和位移张量主值表明席夫碱C = N键是反式的。此外，13C-14化学位移（121.2 ppm）在质子化（C = N反式）席夫碱模型化合物显示的值范围（120-123 ppm）内，表明C = N键是质子化的。我们的结果结合视紫红质中波长调节的机制进行了讨论。
