Downer N W, Cone R A
Biophys J. 1985 Mar;47(3):277-84. doi: 10.1016/S0006-3495(85)83917-5.
If a photoexcited rhodopsin molecule initiates the formation of rhodopsin oligomers during the process of visual excitation, the rate of rotational diffusion of the rhodopsin molecules involved should change markedly. Using microsecond-flash photometry, we have observed the rotational diffusion of rhodopsin throughout the time period of visual excitation and found that no detectable change occurs in its rotational diffusion rate. Partial chemical cross-linking of the retina yields oligomers of rhodopsin and causes a significant decrease in the rotational diffusion rate of rhodopsin even when as little as 20% of rhodopsin is dimeric. Moreover, the pattern of oligomers formed by cross-linking, taken together with the magnitude of decreases in rotational diffusion rate accompanying the cross-linking reaction, suggests that rhodopsin is a monomer in the dark-adapted state. The experiments reported here show that photoexcited rhodopsin molecules do not irreversibly associate with unbleached neighbors during the time course of the receptor response. Hence, it is not likely that stable oligomers of rhodopsin trigger the excitation of the photoreceptor cell.
如果一个光激发的视紫红质分子在视觉激发过程中引发视紫红质寡聚体的形成，那么所涉及的视紫红质分子的旋转扩散速率应该会发生显著变化。我们使用微秒级闪光光度法，在整个视觉激发时间段内观察了视紫红质的旋转扩散，发现其旋转扩散速率没有可检测到的变化。视网膜的部分化学交联会产生视紫红质寡聚体，即使只有20%的视紫红质是二聚体，也会导致视紫红质的旋转扩散速率显著降低。此外，交联形成的寡聚体模式，连同交联反应伴随的旋转扩散速率降低的幅度，表明视紫红质在暗适应状态下是单体。此处报道的实验表明，在受体反应过程中，光激发的视紫红质分子不会与未漂白的相邻分子不可逆地结合。因此，视紫红质的稳定寡聚体不太可能触发光感受器细胞的激发。
