Real light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin: light emission from the singlet-excited state of coelenteramide phenolate anion in a contact ion pair
Real light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin: light emission from the singlet-excited state of coelenteramide phenolate anion in a contact ion pair
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DOI：
10.1016/j.tet.2006.04.044
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发表时间：
2006-06-26
期刊：
影响因子：
2.1
通讯作者：
Hirano, Takashi
中科院分区：
文献类型：
--
作者：
Mori, Kotaro;Maki, Shojiro;Hirano, Takashi
系统研究了腔肠酰胺类似物的酚阴离子（3（O）（-））和酰胺阴离子（5（N）（-））与不同抗衡阳离子的离子对荧光，以阐明钙激活的发光蛋白水母发光蛋白和奥贝林生物发光中发光体的离子结构。3（O）-与有机碱的共轭酸（BASE-H+）形成的离子对的荧光性质随离子对的结构变化和溶剂极性而变化。特别是，3（O）-与正丁胺共轭酸离子对（NBA-H+）的荧光表明3（O）（-）（（1）3（O）（-）*）与NBA-H+形成接触离子对，其中3（O）-的荧光发射最大值对溶剂极性和3（O）-的荧光量子产率敏感极性较低溶剂中增加。结果还证实了（1）3（O）-* 是一种扭曲的分子内电荷转移态。相比之下，离子对中5（N）（-）的荧光几乎不依赖于BASE-H+或溶剂极性。基于这些结果，我们得出结论，发光体在水母发光蛋白和奥贝林生物发光是单重激发态的腔肠酰胺酚阴离子2（O）（-）（（1）2（O）（-）*）的接触离子对与咪唑侧链的组氨酸残基，这是位于极性较低的活性位点的发光蛋白。我们还提出了生物发光反应的机理，包括化学激发过程，得到（1）2（O）（-）*. (c)2006爱思唯尔有限公司保留所有权利。
Fluorescence of the phenolate anion (3(O)(-)) and the amide anion (5(N)(-)) of coelenteramide analogues in ion pairs with various counter cations was systematically investigated to elucidate the ionic structure of the light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin. The fluorescent properties of 3(O)- in an ion pair with a conjugate acid of an organic base (BASE-H+) were varied depending on the structural variation of the ion pair and the solvent polarity. In particular, the fluorescence of 3(O)- in the ion pair with the conjugate acid of n-butylamine (NBA-H+) indicates that the singlet-excited state of 3(O)(-) ((1)3(O)(-)*) and NBA-H+ make a contact ion pair in which the fluorescence emission maxima of 3(O)- is sensitive to the solvent polarity and the fluorescence quantum yields of 3(O)- increase in a less polar solvent. The results also confirm that (1)3(O)-* is a twisted intramolecular charge transfer state. By contrast, the fluorescence of 5(N)(-) in an ion pair depends little on the BASE-H+ or the solvent polarity. Based on these results, we conclude that the light emitter in aequorin and obelin bioluminescences is the singlet-excited state of coelenteramide phenolate anion 2(O)(-)((1)2(O)(-)*) in a contact ion pair with an imidazolium side chain of a histidine residue, which is located at the less polar active sites of the photoproteins. We also propose a mechanism for the bioluminescence reaction, including the chemiexcitation process to give (1)2(O)(-)*. (c) 2006 Elsevier Ltd. All rights reserved.