de Grip W J, Gillespie J, Rothschild K J
Biochim Biophys Acta. 1985 Aug 28;809(1):97-106. doi: 10.1016/0005-2728(85)90172-0.
Structural changes due to photoreceptor membrane bleaching can be studied by Fourier transform infrared difference spectroscopy [1,2]. In this paper we focus on the differences between rhodopsin and metarhodopsin I or II. Peaks in the 1700-1770 cm-1 region are observed, which may be produced by carbonyl groups in either carboxyl (COOH) or ester carbonyl (COOC) groups, the latter being found exclusively in membrane lipids. In order to distinguish between these two types of carbonyl groups, we have studied reconstituted membranes of rhodopsin in a synthetic phosphatidylcholine that lacks ester carbonyl groups. On this basis, we conclude that the major changes in this region are due to rhodopsin carboxyls which undergo either a change in local environment or a protonation/deprotonation reaction. Additional small changes in this region may reflect a direct involvement of phospholipids in the metarhodopsin I-to-II transition. One or more groups responsible for peaks near 1727 and 1702 cm-1 are inaccessible to the outside medium according to hydrogen/deuterium exchange. In contrast, carboxyl group(s) producing peaks near 1710, 1745 and 1768 cm-1 exchange freely with the outside medium and are therefore likely to be located near the membrane surface. Removal of a portion of the C-terminal tail region using proteinase K demonstrates that the carboxyl groups in the C-terminal sequence 248-348 are not involved directly in the rhodopsin to metarhodopsin II transition. At the meta I stage, only carboxyl peaks associated with buried groups appear, suggesting that the initial bleaching events, leading to the formation of this intermediate, produce structural rearrangements in the interior region of rhodopsin. These changes then spread to the peripheral surface regions during the metarhodopsin I-to-II transition.
由于光感受器膜漂白引起的结构变化可以通过傅里叶变换红外差光谱法进行研究[1,2]。在本文中，我们重点关注视紫红质与视紫红质I或II之间的差异。在1700 - 1770 cm-1区域观察到峰值，这可能由羧基（COOH）或酯羰基（COOC）中的羰基产生，后者仅存在于膜脂中。为了区分这两种类型的羰基，我们研究了视紫红质在缺乏酯羰基的合成磷脂酰胆碱中的重构膜。在此基础上，我们得出结论，该区域的主要变化是由于视紫红质羧基经历了局部环境的变化或质子化/去质子化反应。该区域的其他小变化可能反映了磷脂在视紫红质I向II转变中的直接参与。根据氢/氘交换，负责1727和1702 cm-1附近峰值的一个或多个基团对外部介质不可达。相比之下，在1710、1745和1768 cm-1附近产生峰值的羧基可与外部介质自由交换，因此可能位于膜表面附近。使用蛋白酶K去除一部分C末端尾部区域表明，C末端序列248 - 348中的羧基不直接参与视紫红质向视紫红质II的转变。在视紫红质I阶段，仅出现与埋藏基团相关的羧基峰，这表明导致该中间体形成的初始漂白事件在视紫红质的内部区域产生了结构重排。这些变化然后在视紫红质I向II的转变过程中扩散到外周表面区域。
