Chloride effect on the early photolysis intermediates of a gecko cone-type visual pigment.
Chloride effect on the early photolysis intermediates of a gecko cone-type visual pigment.
复制标题
氯化物对壁虎视锥型视色素早期光解中间体的影响。
DOI：
10.1021/bi00017a013
复制
发表时间：
1995
期刊：
影响因子：
2.9
通讯作者：
Kliger,DS
中科院分区：
文献类型：
--
作者：
Lewis,JW;Liang,J;Ebrey,TG;Sheves,M;Kliger,DS
1994年12月5日收到的修订版Mandalpt ®摘要：对含有生理氯离子水平的Tokay壁虎（Gekko gekko）视网膜的毛地黄皂苷提取物中的锥型视觉色素P521进行了纳秒激光光解测量，并对已耗尽氯离子或含有高水平（4 M）氯离子的样品进行了测量。在用532-或477-nm光化光脉冲激发后，以30 ns至60 µ s的时间延迟序列记录吸光度差光谱。全局分析表明，在所有氯化物条件下，壁虎色素P521的动力学衰减数据最适合于两个指数过程。检测到的初始光产物具有宽光谱特性，其为一种平衡混合物，该混合物是一种蓝移中间体（BSI P521）衰变产物的中间体。第一个指数过程被分配给该混合物衰变为Lumi P521中间体。第二个指数过程被确定为Lumi P521到Meta Ip 521的衰减。初始光产物的光谱表现出对氯化物浓度的强烈依赖性，表明氯化物影响了BSP 521和BSI P521的平衡混合物的组成。这些结果表明，对氯离子的亲和力在BSP 521中间体中降低约5倍，在BSI P521中间体中降低约50倍。氯化物浓度也影响平衡混合物的表观衰减速率。当表观衰变率按平衡混合物的组成进行校正时，得到了一个相对不变的BSI衰变微观速率常数（k= 1/55 ns-1）。所测得的速率常数与合成的9-czj-a-视网膜壁虎色素的平衡混合物完全前移的结果一致，表明BSI衰减受一个弛豫过程控制，与发色团和氯离子浓度无关，因此推测是壁虎视蛋白的特征。视杆细胞在昏暗的照明条件下提供视觉信息，而视锥细胞提供在更明亮的光下可获得的更高水平的视觉信息。尽管人们对视紫红质（大多数视杆细胞的视色素）吸收光后发生的过程了解很多，但对视锥细胞视色素光解后出现的中间物质却知之甚少。许多因素有利于研究视杆细胞。这些包括视锥色素相对于视紫红质的稳定性降低以及视紫红质相对于最容易获得的（例如，牛）视网膜中的视锥色素的大量丰度。另一个重要因素是视网膜中通常存在几种不同的具有不同吸收光谱的锥状色素，并且难以制备用于光化学研究的单个锥状色素。
Revised Manuscript Received December 5, 1994® abstract: Nanosecond laser photolysis measurements were conducted on the cone-type visual pigment P521 in digitonin extracts of Tokay gecko (Gekko gekko) retina containing physiological chloride ion levels and also on samples which had been chloride depleted or which contained high levels (4 M) of chloride. Absorbance difference spectra were recorded at a sequence of time delays from 30 ns to 60 µ& following excitation with a pulse of either 532-or 477-nm actinic light. Global analysis showedthe kinetic decay data for gecko pigment P521 to be best fit by two exponential processes under all chloride conditions. The initial photoproduct detected had a broad spectrum characteristic of an equilibrated mixture of a Batho P521 intermediate with its blue-shifted intermediate (BSI P521) decay product. The first exponential process was assigned to the decay of this mixture to the Lumi P521 intermediate. The second exponential process was identified as the decay of Lumi P521 to Meta Ip521. The initial photoproduct’s spectrum exhibited a strong dependence on chloride concentration, indicating that chloride affectsthe composition of the equilibrated mixture of Batho P521 and BSI P521. These results suggest that the affinity for chloride is reduced~ 5-fold in the Batho P521 intermediate and~ 50-fold in the BSI P521 intermediate. Chloride concentration also affects the apparent decay rate of the equilibrated mixture. When the apparent decayrate is corrected for the composition of the equilibratedmixture, a relatively invariant microscopic rate constant is obtained for BSI decay (k= 1/55 ns-1). The rate constantobtained agrees with the value observed for the synthetic9-czj-a-retinal gecko pigment which has a completely forward-shifted equilibrium mixture, indicating thatthe BSI decay is controlled by a relaxation process independent of chromophore and chloride concentration and thus presumably characteristic of the gecko opsin protein.Two types of receptor cells can typically be found in vertebrate retinas. Rod cells provide visual information under conditions of dim illumination, while cone cells provide the higher level visual information obtainable in brighter light. Whereas a good deal has been learned regarding theprocesses which occur after light is absorbed by rhodopsin, the visualpigment of most rod cells, little is known about the intermediate species which appear after photolysis of the cone cell visual pigments. A number of factors favor study of rod cells. These include the reduced stability of cone pigments relative to rhodopsin and the vast abundance of rhodopsin compared to cone pigments in most easily available (eg, bovine) retinas. Another significant factor is that there are usually several different cone pigments with distinctabsorption spectra present in the retina, and it is difficult to prepare individual cone pigments for photochemical study.