All-trans-retinyl esters are the substrates for isomerization in the vertebrate visual cycle
All-trans-retinyl esters are the substrates for isomerization in the vertebrate visual cycle
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DOI：
10.1021/bi0341004
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发表时间：
2003-05-20
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：
Gollapalli, DR;Rando, RR
在视觉周期的运作过程中，进行反式到顺式异构化产生11-顺式-视黄醇的关键酶的鉴定仍然是难以捉摸的。关于异构化底物的确切性质，文献中存在混淆。争论的焦点是它是全反式视黄酯还是全反式视黄醇（维生素A）。由于这两种假定的底物在视网膜色素上皮细胞膜中迅速相互转化，因此底物的选择可能是模糊的。影响全反式视黄醇和全反式视黄酯相互转化的两种酶是卵磷脂视黄醇酰基转移酶（LRAT）和视黄酯水解酶（REH）。视黄酯或全反式视黄醇池在LRAT和REH抑制剂存在下分别进行放射性标记，有效防止它们的相互转化。脉冲追踪实验明确表明，全反式视黄酯，而不是全反式视黄醇，是11-顺式-视黄醇的前体。当全反式视黄酯池被放射性标记时，所得的11-顺式-视黄醇被标记为具有与前体酯相同的比活性。维生素A的情况正好相反。这些数据明确地确立了全反式视黄酯作为11-顺式-视黄醇的前体。
The identification of the critical enzyme(s) that carries out the trans to cis isomerization producing 11-cis-retinol during the operation of the visual cycle remains elusive. Confusion exists in the literature as to the exact nature of the isomerization substrate. At issue is whether it is an all-trans-retinyl ester or all-trans-retinol (vitamin A). As both putative substrates interconvert rapidly in retinal pigment epithelial membranes, the choice of substrate can be ambiguous. The two enzymes that effect interconversion of all-trans-retinol and all-trans-retinyl esters are lecithin retinol acyl transferase (LRAT) and retinyl ester hydrolase (REH). The retinyl ester or all-trans-retinol pools are radioactively labeled separately in the presence of inhibitors of LRAT and REH, effectively preventing their interconversion. Pulse-chase experiments unambiguously demonstrate that all-trans-retinyl esters, and not all-trans-retinol, are the precursors of 11-cis-retinol. When the all-trans-retinyl ester pool is radioactively labeled, the resulting 11-cis-retinol is labeled with the same specific activity as the precursor ester. The converse is true with vitamin A. These data unambiguously establish all-trans-retinyl esters as the precursors of 11-cis-retinol.