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Molecular Mechanism of Photoreception in Cones.

视锥细胞感光的分子机制。

基本信息

批准号：
03454559
负责人：
SHICHIDA Yoshinori
金额：
$ 4.03万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1993
项目状态：
已结题

项目摘要

The present studies focused on the molecular properties and photochemical reactions of visual pigments in order to elucidate how the difference in light response between rods and cones can be explained on the basis of visual pigments.1. Using a cDNA cloning technique, we have isolated four kinds of cDNA clones encoding chicken cone visual pigments and two clones encoding nocturnal gecko visual pigments. The amino acid residues responsible for the spectral tuning of the visual pigments were speculated on the basis of the differences in amino acid sequence among the visual pigments. A phylogenetic tree of vertebrate visual pigments was then constructed on the basis of amino acid identity. It indicated that an ancestral visual pigment evolved first into four groups of cone visual pigments and that group of rhodopsins, the rod visual pigments, diverged later from one of the four groups. Thus, it is suggested that animals had acquired first the ability to distinguish color and then acquired scotopic vision.2. We have investigated the bleaching process of iodopsin by means of low temperature spectroscopy and laser photolyses. The results showed that iodopsin has similar intermediates corresponding to photo-, batho-, BL, lumi, meta I-, and meta II-intermediates of rhodopsin in its bleaching prosess. Furthemore, like metarhodopsin II, metaiodopsin II has a binding ability to transducin, suggesting that it has a physiological role similar to metarhodopsin II.Comparative studies of cone visual pigments, iodopsin, chicken green and chicken blue with the rod visual pigment rhodopsin clearly showed that cone visual pigments are faster than rhodopsin in rate of regeneration from 11-cis-retinal and opsin, and those of formation and decay of physiologically active intermediate (meta II-intermediate). These difference closely correlate to faster dark-adaptation, faster light response and less photosensitivity of cones than rods, respectively.

本研究主要集中在视色素的分子特性和光化学反应上，以阐明如何根据视色素来解释视杆细胞和视锥细胞之间的光响应差异。 1．利用cDNA克隆技术，我们分离出四种编码鸡锥视色素的cDNA克隆和两种编码夜行性壁虎视色素的cDNA克隆。根据视色素之间氨基酸序列的差异推测负责视色素光谱调节的氨基酸残基。然后根据氨基酸同一性构建了脊椎动物视觉色素的系统发育树。它表明，一种祖先视觉色素首先进化成四组视锥视觉色素，而视紫质（视杆视色素）组后来从这四组视色素中的一组分化出来。由此可见，动物首先获得了辨别颜色的能力，然后获得了暗视能力。2．我们通过低温光谱和激光光解研究了碘紫红质的漂白过程。结果表明，碘紫红质在漂白过程中具有与视紫红质的photo-、batho-、BL、lumi、meta I-和met II-中间体类似的中间体。此外，与变视紫红质一样，变视紫红质II也具有与转导蛋白结合的能力，这表明它具有与变视紫红质II相似的生理作用。对视锥视色素、碘紫红质、鸡绿和鸡蓝与视杆视色素视紫红质的比较研究清楚地表明，视锥视色素从11-顺式视黄醛和视蛋白再生的速度比视紫红质快，而视紫红质的再生速度比视紫红质快。生理活性中间体（meta II-中间体）的形成和衰变。这些差异分别与视锥细胞比视杆细胞更快的暗适应、更快的光响应和更低的光敏性密切相关。