Earnest T N, Roepe P, Braiman M S, Gillespie J, Rothschild K J
Biochemistry. 1986 Dec 2;25(24):7793-8. doi: 10.1021/bi00372a002.
Polarized, low-temperature Fourier transform infrared (FTIR) difference spectroscopy has been used to investigate the structure of bacteriorhodopsin (bR) as it undergoes phototransitions from the light-adapted state, bR570, to the K630 and M412 intermediates. The orientations of specific retinal chromophore and protein groups relative to the membrane plane were calculated from the linear dichroism of the infrared bands, which correspond to the vibrational modes of those groups. The linear dichroism of the chromophore C=C and C-C stretching modes indicates that the long axis of the polyene chain is oriented at 20-25 degrees from the membrane plane at 250 K and that it orients more in-plane when the temperature is reduced to 81 K. The polyene plane is found to be approximately perpendicular to the membrane plane from the linear dichroism calculations of the HOOP (hydrogen out-of-plane) wags. The orientation of the transition dipole moments of chromophore vibrations in the K630 and M412 intermediates has been probed, and the dipole moment direction of the C=O bond of an aspartic acid that is protonated in the bR570----M412 transition has been measured.
偏振低温傅里叶变换红外（FTIR）差示光谱已被用于研究细菌视紫红质（bR）从光适应状态bR570向K630和M412中间体进行光转变时的结构。特定视网膜发色团和蛋白质基团相对于膜平面的取向是根据红外波段的线性二色性计算得出的，这些波段对应于这些基团的振动模式。发色团C=C和C-C伸缩模式的线性二色性表明，在250K时，多烯链的长轴与膜平面呈20 - 25度角取向，当温度降至81K时，其取向更偏向平面内。从HOOP（氢出平面）摆动的线性二色性计算发现，多烯平面大致垂直于膜平面。已探测了K630和M412中间体中发色团振动的跃迁偶极矩的取向，并测量了在bR570→M412转变中质子化的天冬氨酸的C=O键的偶极矩方向。
