Foster K W, Saranak J, Dowben P A
Department of Physics, Syracuse University, NY 13244-1130.
J Photochem Photobiol B. 1991 Mar;8(4):385-408. doi: 10.1016/1011-1344(91)80114-w.
Retinal normally binds opsin forming the chromophore of the visual pigment, rhodopsin. In this investigation synthetic analogs were bound by the opsin of living cells of the alga Chlamydomonas reinhardtii; the effect was assayed by phototaxis to give an activation spectrum for each rhodopsin analog. The results show the influence of different chromophores and the protein on the absorption of light. The maxima of the phototaxis action spectra shifted systematically with the number of double bonds conjugated with the imine (C = N+H) bond of the chromophore. Chromophores lacking a beta-ionone ring, methyl groups and all C = C double bonds photoactivated the rhodopsin of Chlamydomonas with normal efficiency. On the basis of a simple model involving one-electron transitions between occupied and virtual molecular orbitals, we estimate the charge distribution along the chromophore in the binding site. With this restraint we define a unique structural model for eukaryotic rhodopsins and explain the spectral clustering of pigments, the spectral differences between red and green rhodopsins and the molecular basis of color blindness. Our results are consistent with the triggering of the activation of rhodopsin by the light-mediated change in electric dipole moment rather than the steric cis-trans isomerization of the chromophore.
视黄醛通常与视蛋白结合，形成视觉色素视紫红质的发色团。在本研究中，合成类似物被莱茵衣藻活细胞的视蛋白所结合；通过趋光性测定其效果，以给出每种视紫红质类似物的激活光谱。结果显示了不同发色团和蛋白质对光吸收的影响。趋光性作用光谱的最大值随着与发色团的亚胺（C = N+H）键共轭的双键数量而系统地移动。缺乏β-紫罗兰酮环、甲基和所有C = C双键的发色团能以正常效率光激活衣藻的视紫红质。基于一个涉及占据和虚拟分子轨道之间单电子跃迁的简单模型，我们估计了结合位点中沿发色团的电荷分布。在此限制下，我们定义了真核视紫红质的独特结构模型，并解释了色素的光谱聚类、红色和绿色视紫红质之间的光谱差异以及色盲的分子基础。我们的结果与视紫红质的激活是由光介导的电偶极矩变化而非发色团的空间顺反异构化触发这一观点一致。
