Molecular basis on the functional difference between rods and cones

视杆细胞和视锥细胞功能差异的分子基础

基本信息

批准号：
15370068
负责人：
KAWAMURA Satoru
金额：
$ 8.32万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15370068/
关键词：
rod cone GRK1 GRK7 visual pigment phosphorylation 視物質リン酸化キナーゼ光応答

项目摘要

Cone photoreceptors show briefer photoresponses than rod photoreceptors. Our previous study showed that visual pigment phosphorylation, a quenching mechanism of light-activated visual pigment, is much more rapid in cones than in rods (Tachibanaki et al., Proc.Nati.Acad Sci.USA, 98,14044-14049,2001). In this project, we measured early time course of this rapid phosphorylation with a newly constructed, computer-assisted rapid quench apparatus and directly compared it with the photoresponse time course in cones. At the time of photoresponse recovery, almost two phosphates were found to be incorporated into a bleached cone pigment molecule. This result indicated for the first time that the visual pigment phosphorylation coincides with the photoresponse recovery. The rapid phosphorylation in cones is attributed to a very high activity of visual pigment kinase in cones (GRK7). Because of this high activity, cone pigment is readily phosphorylated at very high bleach levels, which probably explains why cone photoresponses recover quickly even after a very bright light and do not saturate under intense background light. On the other hand, phosphorylation of rod visual pigment was already saturated at low bleach levels, which reasonably explains why rods are easily saturated with much weaker light. The high GRK7 activity is brought about by high content of a highly potent enzyme. The expression level of GRK7 was 10 times higher than that of rod kinase (GRK1), and the specific activity of a single GRK7 molecule was about 10 times higher than that of GRK1. The specific activity of GRK7 is the highest among the GRKs so far known. Our result seems to explain the response characteristics of cone photoreceptors in many aspects including the non-saturation of the cone responses during daylight vision.

锥光受体比杆光感受器显示出Briefer光疗。我们先前的研究表明，视觉色素磷酸化是一种光激活视觉色素的淬火机制，锥体的快速速度要比杆子快得多（Tachibanaki等，Proc.nati.Acad Sci.usa，98,140444-14049,2001）。在这个项目中，我们通过新建造的，计算机辅助的快速淬火设备测量了这种快速磷酸化的早期过程，并将其与锥体中的光响应时间课程直接进行了比较。在光增强响应恢复时，发现将近两个磷酸盐掺入了漂白的锥体色素分子中。该结果首次表明视觉色素磷酸化与光响应恢复相吻合。锥体中的快速磷酸化归因于锥体中视觉色素激酶的活性很高（GRK7）。由于这种高活性，因此很容易在非常高的漂白剂水平下磷酸化，这可能解释了为什么即使在非常明亮的光线之后，锥光子也很快恢复，并且在强烈的背景光下也不会饱和。另一方面，杆视觉色素的磷酸化已经在低漂白剂水平下饱和，这合理地解释了为什么杆很容易被较弱的光饱和。高GRK7活性是由高含量高的酶带来的。 GRK7的表达水平比Rod激酶（GRK1）高10倍，单个GRK7分子的比活性比GRK1高约10倍。迄今为止，GRK7的特定活性是GRK中最高的活性。我们的结果似乎解释了许多方面的锥光感受体的响应特征，包括在白天视觉中锥反应的不饱和。