Retinal Shuttle Protein and Visual Photoreception

在软体动物中，视力是通过两种感光剂的光反应来维持的。视紫红质存在于视觉细胞外段的横纹体中，视黄素存在于内段的髓样小体中。视网膜结合蛋白(RALBP)和它的偏色素之间的相互交换支持着每种光色素的再生。我们研究了RALBP在视紫红质-视黄素结合系统中的作用如下。RALBP的免疫细胞化学定位：用多克隆和单克隆抗体在电子显微镜下观察RALBP的详细定位。在外段，最明显的抗RALBP标记出现在核心细胞质的包膜上，对应于横纹体微绒毛的基底缘。在内段，髓小体的整个表面都有明显的标记，但线粒体和细胞核中的标记很少。眼球的光再生和RALBP：基于…中的前一次更多的体外实验，在照射眼罩后的黑暗孵育期间，检查了RALBP在完整视网膜中实际移动的细节。显然，RALBP能够作为顺式和反式视网膜的穿梭车在视觉细胞内移动，并将它们交换为视紫红质和视黄色素的再生色素，以帮助视紫红质和视黄色素的再生。RALBP和视色素之间的视网膜交换机制：为了解决这个问题，我们特别感兴趣的是比较视紫红质、视黄色素和RALBP在一个物种Todarodes中的蛋白质结构。我们测定了视黄素和RALBP的氨基酸序列。视黄素由301个氨基酸组成，相对分子质量为33,490。亲水性分析表明，它被折叠成7个疏水跨膜片段，与视紫红质相似。视黄醇脱氢酶：RALBP除了与视网膜结合外，还能结合相当数量的11-顺式视黄醇。当与视网膜膜制剂孵育时，RALBP的11-顺式视黄醇配体改变为11-顺式视黄醇，而不从蛋白中释放。内节的远端活性最高。这与髓样小体的分布相似。较少

In Mollusca, vision is maintained by the photoreactions of two photopigments. Rhodopsin is present in the rhabdomeres of the outer segment of the visual cell and retinochrome is in the myeloid bodies of the inner segment. Regeneration of each photopigment is supported by the mutual exchange of retinal between a retinal-binding protein (RALBP) and its metapigment. We have examined the role of RALBP in the rhodopsin-retinochrome conjugate system as follows.Immunocytochemical Localization of RALBP : Detailed localization of RALBP was observed electron-microscopically by using poly- and mono-clonal antibodies. In the outer segment, the most marked anti-RALBP labelling appeared along the envelope of core cytoplasm, corresponding to the basal margins of rhabdomeric microvilli. In the inner segment, the labelling was obvious on the entire surface of the myeloid bodies, but scanty in the mitochondria and the nucleus.Photopigment Regeneration and RALBP in the Eyecup : Based upon the previous in … More vitro experiments, details of the actual movement of RALBP in the intact retina was examined during dark incubation following irradiation of the eyecup. It was clear that RALBP is capable of moving within the visual cell as a shuttle of cis and trans retinals, and of exchanging them for metapigment chromophores to assist in the regeneration of rhodopsin and retinochrome.Mechanism of Retinal Exchange between RALBP and Metapigments : To resolve this problem, we have special interest in comparing protein structures of rhodopsin, retinochrome and RALBP in one species, Todarodes. We have determined amino acid sequence of retinochrome as well as RALBP. Retinochrome consists of 301 amino acids with a M.W. of 33,490. The hydropathicity analysis showed that it is folded into 7 hydrophobic transmembrane segments, just like rhodopsins.Retinol-dehydrogenase : RALBP binds appreciable quantities of 11-cis-retinol in addition to retinal. When incubated with a membrane preparation of the retina 11-cis-retinol ligand of RALBP was changed to 11-cis-retinal without releasing from the protein. The highest activity was found in the distal portion of the inner segment. This was similar to the distribution of the myeloid bodies. Less