TAUTOMERIC FORMS OF METARHODOPSIN.
TAUTOMERIC FORMS OF METARHODOPSIN.
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DOI：
10.1085/jgp.47.2.215
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发表时间：
1963-11
期刊：
影响因子：
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通讯作者：
WALD G
中科院分区：
文献类型：
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作者：
MATTHEWS RG;HUBBARD R;BROWN PK;WALD G
光将视紫红质的发色团11-顺式视黄醛（以前的视黄烯）异构化为全反式构型。这引入了一系列不稳定的中间体-前视紫红质、视紫红质、视紫红质，其中全反式视黄醛仍然附着在视蛋白的发色位点上。最后，从视蛋白中水解出视黄醛。目前的实验表明，变视紫红质以两种互变异构形式存在，即变视紫红质I和II，λmax分别为478和380 mµ。后视紫红质I首先出现，然后与后视紫红质II进入平衡。在这种平衡中，较高的温度或pH值、中性盐和甘油有利于变视紫红质II的比例。从变视紫红质I到II的变化涉及质子与pK 6.4的基团（咪唑？）的结合，以及熵的大幅增加。Metarhodopsin II在早期被混淆为全反式视网膜和视蛋白的最终混合物（λmax 387 mµ），它在光谱上类似。然而，这两种产物在实验上很容易区分。
Light isomerizes the chromophore of rhodopsin, 11-cis retinal (formerly retinene), to the all-trans configuration. This introduces a succession of unstable intermediates—pre-lumirhodopsin, lumirhodopsin, metarhodopsin —in which all-trans retinal is still attached to the chromophoric site on opsin. Finally, retinal is hydrolyzed from opsin. The present experiments show that metarhodopsin exists in two tautomeric forms, metarhodopsins I and II, with λmax 478 and 380 mµ. Metarhodopsin I appears first, then enters into equilibrium with metarhodopsin II. In this equilibrium, the proportion of metarhodopsin II is favored by higher temperature or pH, neutral salts, and glycerol. The change from metarhodopsin I to II involves the binding of a proton by a group with pK 6.4 (imidazole?), and a large increase of entropy. Metarhodopsin II has been confused earlier with the final mixture of all-trans retinal and opsin (λmax 387 mµ), which it resembles in spectrum. These two products are, however, readily distinguished experimentally.