Makino C L, Groesbeek M, Lugtenburg J, Baylor D A
Department of Ophthalmology, Harvard Medical School, and the Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA.
Biophys J. 1999 Aug;77(2):1024-35. doi: 10.1016/S0006-3495(99)76953-5.
In visual pigments, opsin proteins regulate the spectral absorption of a retinal chromophore by mechanisms that change the energy level of the excited electronic state relative to the ground state. We have studied these mechanisms by using photocurrent recording to measure the spectral sensitivities of individual red rods and red (long-wavelength-sensitive) and blue (short-wavelength-sensitive) cones of salamander before and after replacing the native 3-dehydro 11-cis retinal chromophore with retinal analogs: 11-cis retinal, 3-dehydro 9-cis retinal, 9-cis retinal, and 5,6-dihydro 9-cis retinal. The protonated Schiff's bases of analogs with unsaturated bonds in the ring had broader spectra than the same chromophores bound to opsins. Saturation of the bonds in the ring reduced the spectral bandwidths of the protonated Schiff's bases and the opsin-bound chromophores and made them similar to each other. This indicates that torsion of the ring produces spectral broadening and that torsion is limited by opsin. Saturating the 5,6 double bond in retinal reduced the perturbation of the chromophore by opsin in red and in blue cones but not in red rods. Thus an interaction between opsin and the chromophoric ring shifts the spectral maxima of the red and blue cone pigments, but not that of the red rod pigment.
在视觉色素中，视蛋白通过改变激发电子态相对于基态的能量水平的机制来调节视黄醛发色团的光谱吸收。我们通过光电流记录来研究这些机制，以测量在将天然的3-脱氢11-顺式视黄醛发色团替换为视黄醛类似物（11-顺式视黄醛、3-脱氢9-顺式视黄醛、9-顺式视黄醛和5,6-二氢9-顺式视黄醛）前后，蝾螈单个红色视杆以及红色（长波长敏感型）和蓝色（短波长敏感型）视锥的光谱敏感性。与结合到视蛋白上的相同发色团相比，环中具有不饱和键的类似物的质子化席夫碱具有更宽的光谱。环中键的饱和降低了质子化席夫碱和视蛋白结合的发色团的光谱带宽，并使它们彼此相似。这表明环的扭转会导致光谱展宽，并且扭转受到视蛋白的限制。使视黄醛中的5,6双键饱和减少了视蛋白对红色和蓝色视锥中发色团的扰动，但对红色视杆中的发色团没有影响。因此，视蛋白与发色团环之间的相互作用会使红色和蓝色视锥色素的光谱最大值发生偏移，但不会使红色视杆色素的光谱最大值发生偏移。
