Retinal Shuttle Protein and Visual Photoreception

在软体动物中，视觉是通过两种色素的光反应来维持的。视紫红质存在于视细胞外节的横纹中，视色素存在于内节的髓样体中。每种色素的再生都是由视网膜结合蛋白（RALBP）和其变性色素之间的视网膜相互交换支持的。RALBP在视紫红质-视黄色素结合系统中的作用如下：RALBP的免疫细胞化学定位：用多克隆抗体和单克隆抗体在电子显微镜下观察RALBP的详细定位。在外节，最显着的抗RALBP标记出现沿着核心细胞质的包膜，对应于横纹肌微绒毛的基底边缘。内节髓样小体表面标记明显，线粒体和细胞核标记较少。 ...更多信息 在体外实验中，在照射眼杯后的黑暗孵育期间检查RALBP在完整视网膜中的实际运动的细节。很明显，RALBP是能够在视觉细胞内移动的穿梭的顺式和反式视网膜，并交换他们的metapigment发色团，以协助再生的视紫红质和retinochrome.Mechanism的RALBP和Metapigments之间的视网膜交换：为了解决这个问题，我们有特别的兴趣在比较蛋白质结构的视紫红质，retinochrome. RALBP在一个物种，Todarodes。我们测定了维甲酸色素和RALBP的氨基酸序列。视网膜色素由301个氨基酸组成，分子量为10000。33490人。疏水性分析表明，RALBP与视紫红质一样，折叠成7个疏水性跨膜片段。当与视网膜的膜制备物一起孵育时，RALBP的11-顺式-视黄醇配体变为11-顺式-视黄醇，而不从蛋白质中释放。最高的活动被发现在内段的远端部分。这与髓样小体的分布相似。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