Aton B, Doukas A G, Narva D, Callender R H, Dinur U, Honig B
Biophys J. 1980 Jan;29(1):79-94. doi: 10.1016/S0006-3495(80)85119-8.
Resonance Raman multicomponent spectra of bovine rhodopsin, isorhodopsin, and bathorhodopsin have been obtained at low temperature. Application of the double beam "pump-probe" technique allows us to extract a complete bathorhodopsin spectrum from the mixture in both protonated and deuterated media. Our results show that the Schiff base of bathorhodopsin is fully protonated and that the extent of protonation is unaffected by its photochemical formation from either rhodopsin or isorhodopsin. The Raman spectrum of bathorhodopsin is significantly different than that of either parent pigment, thus supporting the notion that a geometric change in the chromophore is an important component of the primary photochemical event in vision. A normal mode analysis is carried out with particular attention devoted to the factors that determine the frequency of the C=N stretching vibration. We find that the increased frequency of this mode in protonated relative to unprotonated Schiff bases is due to coupling between C=N stretching and C=N-H bending motions, and the shift observed upon deuteration of the Schiff base can also be understood in these terms. Various models for the primary event are discussed in light of our experimental and theoretical results.
已在低温下获得了牛视紫红质、异视紫红质和视紫红质原的共振拉曼多组分光谱。采用双光束“泵浦-探测”技术使我们能够从质子化和氘代介质中的混合物中提取完整的视紫红质原光谱。我们的结果表明，视紫红质原的席夫碱完全质子化，且质子化程度不受其由视紫红质或异视紫红质光化学形成过程的影响。视紫红质原的拉曼光谱与任何一种母体色素的光谱都有显著差异，因此支持了发色团的几何变化是视觉中初级光化学事件的一个重要组成部分这一观点。进行了简正模式分析，特别关注了决定C=N伸缩振动频率的因素。我们发现，相对于未质子化的席夫碱，质子化席夫碱中该模式频率的增加是由于C=N伸缩与C=N-H弯曲运动之间的耦合，并且席夫碱氘代时观察到的位移也可以用这些术语来理解。根据我们的实验和理论结果讨论了初级事件的各种模型。
