A MECHANISM FOR CONTROLLING THE PK(A) OF THE RETINAL PROTONATED SCHIFF-BASE IN RETINAL PROTEINS - A STUDY WITH MODEL COMPOUNDS
A MECHANISM FOR CONTROLLING THE PK(A) OF THE RETINAL PROTONATED SCHIFF-BASE IN RETINAL PROTEINS - A STUDY WITH MODEL COMPOUNDS
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DOI：
10.1021/ja00062a052
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发表时间：
1993-05-05
影响因子：
15
通讯作者：
SHEVES, M
中科院分区：
文献类型：
--
作者：
GAT, Y;SHEVES, M
膜蛋白色素视紫红质负责多种光生物学功能，如视觉转导（视紫红质，Rh），光合作用（细菌视紫红质，bR和盐视紫红质），趋光性（感觉视紫红质）和光异构化（视黄色素）。所有这些视紫红质都由类似的视黄基多烯（bR为全反式，Rh为11顺式）组成，通过质子化的希夫碱与赖氨酸e-氨基结合到视蛋白上。光吸收引起一系列事件，导致希夫碱去质子化过程。后者对于bR中的质子泵送和视紫红质的激活至关重要。因此，了解控制各种色素及其光化学诱导中间体中视网膜质子化希夫碱pKa的因素至关重要。在bR中，质子化希夫碱的表观pKz为13.3±0.3，而在牛视紫红质中，最近的一项研究指出，表观pKa可能高于16.3。在本研究中，我们证明，通过在质子化希夫碱键和羧酸基之间形成一定的角度，可以显著改变视网膜质子化希夫碱的pK”，从而允许与一个或多个桥接这两个基团的水分子有效相互作用。全反式视网膜用三氟乙醇浓缩
The membrane protein pigments rhodopsins are responsible for a variety of photobiological functions, such as visual transduction (visual rhodopsins, Rh), photosynthesis (bacteriorhodop-sin, bR, and halorhodopsin), phototaxis (sensory rhodopsin) and photoisomerization (retinochrome). All of these rhodopsins consist of a similar retinyl polyene (all-trans in bR and 11-cis in Rh), bound to the opsin via a protonated Schiff base with a lysine e-amino group. Light absorption induces a sequence of events which lead to a Schiff base deprotonation process. 1 The latter is crucial for the proton pumping in bR and for activating rhodopsin. Thus, understanding the factors that control the pKa of the retinal protonated Schiff base in the various pigments and their photochemically induced intermediates is of primary importance. In bR, an apparent pKz of 13.3±0.3 was observed for the protonated Schiff base, 2 whereas in bovine rhodopsin a recent work pointed to the possibilityof apparent pKa higher than 16.3In the present study, we demonstrate that the pK „of retinal protonated Schiff base can be significantly alteredby forming a definite anglebetween the protonated Schiff base linkage and a carboxylate group which allows for effective interaction with one or more water molecules bridging the two groups. All-trans retinal was condensed in trifluoroethanol with