Biosynthesis of 11-cis-retinoids and retinyl esters by bovine pigment epithelium membranes.
Biosynthesis of 11-cis-retinoids and retinyl esters by bovine pigment epithelium membranes.
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牛色素上皮膜生物合成 11-顺式视黄醇和视黄酯。
DOI：
10.1021/bi00398a059
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发表时间：
1987
期刊：
影响因子：
2.9
通讯作者：
Rando,RR
中科院分区：
文献类型：
--
作者：
Fulton,BS;Rando,RR
生物化学和分子药理学系，哈佛医学院，波士顿，马萨诸塞州02115 1987年5月6日接收; 1987年7月20日接收修订的Mannipt摘要：以前，我们已经表明来自两栖动物的视网膜/色素上皮膜可以从添加的全反式视黄醇合成1-反式-类维生素A [伯恩斯坦，P.S.，劳，W。C，& Rando，R. R.等人（1987）Proc. Acad. Sci. USA 84，1849-1853]，活性主要定位于色素上皮。这里表明，在牛系统中，活性只存在于色素上皮细胞的膜中。亚细胞分级分离并不能揭示活性所在的特定细胞器。洗过的牛色素膜，这是缺乏类维生素A氧化还原活性，转换添加的11-m-视黄醇和其棕榈酸酯的混合物。α-反式-视黄酸和全反式-视黄基棕榈酸酯不被膜转化为11-顺式-类视黄酸。膜显示出大量的酯合成酶活性，产生大量的全反式-Tctiny\棕榈酸酯。不同的化学试剂，如乙醇，羟胺，和p-（羟汞）苯甲酸酯，抑制酯合成酶和异构酶的活动在一个大致平行的方式，这表明两个活动之间可能的功能联系。视紫红质对光的吸收导致视紫红质的11-m-视网膜席夫碱发色团的顺式到反式异构化（Hubbard & Wald，1952）。全反式四环素1席夫碱在一个称为漂白的过程中水解，产生全反式-色氨酸和视蛋白（Bownds，1967）。为了使视力继续，11-m-视网膜必须通过纯粹的热途径在眼睛中生物合成。构成这一途径的生化反应被认为包括“视觉循环”，并且每当发生大量漂白时，这一循环的功能对于暗适应过程至关重要（Knowles & Dartnall，1977 a）。最近几年已经看到在视觉转导的分子理解方面取得了很大进展，视觉转导是由连接视紫红质对光量子的吸收和视杆细胞外段质膜钠通道的关闭的那些生物化学事件组成的过程（Fung & Stryer，1980;惠勒& Bitensky，1977; Fesenko等人，1985年）。相比之下，对视觉周期的分子或生理理解进展甚微。没有一种酶被纯化，也没有鉴定出任何控制因素。理解这个循环的核心是反式到顺式异构化过程的解开。由于该过程的吸能性质，这里需要的不仅仅是全反式-视黄醛到其11-顺式同系物的简单异构化（Rando & Chang，1983）。在暗适应的眼睛中，超过75%的类维生素A是11-顺式的，而在化学平衡下，它们中只有0.1%是。此外，其他类维生素A也是该循环的一部分，因此异构化过程的底物不需要是游离的全反式-视黄醛，事实上也不是（伯恩斯坦和兰多，1986）。漂白过程中产生的全反式视黄醇在视网膜中迅速还原为全反式视黄醇，然后转运至相邻的色素上皮，在那里酯化并储存为长链脂肪酸酯（Knowles &Dartnall，1977 a）。f由美国国立卫生研究院的美国公共卫生服务研究基金EY 04096支持。信件应寄给这位作者。
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115 Received May 6, 1987; Revised Manuscript Received July 20, 1987 abstract: Previously, we have shown that retina/pigment epithelium membranes from the amphibian can synthesize 1 l-tis-retinoids from added all-trans-retinol [Bernstein, P. S., Law, W. C, & Rando, R. R.(1987) Proc. Natl. Acad. Sci. USA 84, 1849-1853], The activity was largely localized to the pigment epithelium. Here it is shown that, inthe bovine system, the activity resides exclusively in the membranes of the pigment epithelium. Subcellular fractionation does not reveal a particular organelle where the activity resides. Washed bovine pigmentepithelium membranes, which are devoid of retinoid redox activity, convert added allinznj-retinol to a mixture of 11-m-retinol and its palmitate ester. a/Z-rnra-Retinal and all-trans-retinyl palmitate are not converted into 1 l-cfr-retinoids by the membranes. The membranes show substantial ester synthetase activity, producing largeamounts of all-trans-Tctiny\palmitate. Diverse chemical reagents, such as ethanol, hydroxylamine, and p-(hydroxymercuri) benzoate, inhibit both ester synthetase and isomerase activities in a roughly parallel fashion, suggesting a possible functional linkage between the two activities. e absorption of light by rhodopsin results in the cis to trans isomerization of rhodopsin’s 11-m-retinal Schiff base chromophore (Hubbard & Wald, 1952). The all-trans-TCtina. 1 Schiff base is hydrolyzed, producing all-trans-rzÚTt&X and opsin, in a process called bleaching (Bownds, 1967). In order for vision to proceed, 11-m-retinal must be biosynthesized in the eye by a purely thermal pathway. The biochemical reactions that make up this pathway are said to comprise the “visual cycle”, and the functioning of this cycle is critical to the process of dark adaptation whenever substantial bleaching has oc-curred (Knowles & Dartnall, 1977a). The last several years have seen much progress made toward a molecular understanding of visual transduction—a process which is comprised of those biochemical events connecting the absorption of a quantum of light by rhodopsin and the closing of the rod outer segment plasma membrane sodium channels (Fung & Stryer, 1980; Wheeler & Bitensky, 1977; Fesenko et al., 1985). By contrast, very little progress has been made toward either a molecular or a physiologic understanding of the visual cycle. None of the enzymes has been purified nor have any elements of control been identified. Central to an understanding of this cycle is the unravelling of the trans to cis isomerization process. More than a simple isomerization of all-trans-retinal to its 11-cis congener is required here, because of the endergonic nature of the process (Rando & Chang, 1983). In a dark-adapted eye, greater than 75% of the retinoids are 11-cis, whereas at chemical equilibrium only 0.1% of them are. In addition, other retinoids are part of the cycle, so that the substrate for the isomerization process need not be free all-trans-retinal and, in fact, is not (Bernstein & Rando, 1986). The all-trans-retinal produced from the bleaching process is rapidly reduced in the retina to allfrani-retinol, which is then transported to the adjoining pig-ment epithelium, where it is esterified and stored as long-chain fatty acid esters (Knowles &Dartnall, 1977a). f Supported by US Public Health Service Research Grant EY04096 from the National Institutes of Health.* Correspondence should be addressed to this author.