Wagner R, Ryba N, Uhl R
Max-Planck-Institut für Biophysikalische Chemie, Göttingen, FRG.
FEBS Lett. 1988 Aug 1;235(1-2):103-8. doi: 10.1016/0014-5793(88)81242-0.
In photoreceptors of the living retina both activation and deactivation of transducin must occur in less than 1 s. In ROS preparations used for in vitro studies, however, deactivation takes minutes. This is due to the fact that activated transducin is released into the free aqueous space, whereby GTPase activity and consequent deactivation of the protein are slowed down, and due to the dilution of soluble ROS proteins involved in the quenching of rhodopsin activity. In this paper, using a convenient, non-invasive light scattering assay, we demonstrate that in an intact stack of disks, where active transducin stays membrane associated and is rapidly deactivated, the activity of rhodopsin can also be quenched in the time range of seconds when soluble ROS proteins are supplemented. Arrestin, the 48 kDa protein of the photoreceptor, is one of the proteins required for rapid recovery, however, it requires the synergistic action of other soluble proteins (besides rhodopsin kinase) in order to exert its effect: When arrestin is included in the reaction mixture without the 'helper protein(s)', it cannot speed recovery, and when a mixture of soluble proteins is added which lacks arrestin, there is also no effect. The nature and identity of this (these) helper protein(s) are still unclear.
在活体视网膜的光感受器中，转导蛋白的激活和失活都必须在不到1秒的时间内发生。然而，在用于体外研究的视网膜外段（ROS）制剂中，失活需要数分钟。这是因为激活的转导蛋白释放到自由水相空间中，从而使GTPase活性以及蛋白质的后续失活减慢，并且还因为参与视紫红质活性淬灭的可溶性ROS蛋白被稀释。在本文中，我们使用一种便捷的、非侵入性的光散射测定法证明，在完整的盘状堆叠中，活性转导蛋白与膜结合并迅速失活，当补充可溶性ROS蛋白时，视紫红质的活性也能在数秒的时间范围内被淬灭。抑制蛋白是光感受器中的48 kDa蛋白，是快速恢复所需的蛋白质之一，然而，它需要其他可溶性蛋白（除视紫红质激酶外）的协同作用才能发挥其作用：当抑制蛋白包含在反应混合物中而没有“辅助蛋白”时，它无法加速恢复，并且当添加缺乏抑制蛋白的可溶性蛋白混合物时，也没有效果。这种（这些）辅助蛋白的性质和身份仍然不清楚。
