Absorption Spectra and Photochemical Reactions in a Unique Photoactive Protein, Middle Rhodopsin MR

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• 作者：Keiichi Inoue ; Louisa Reissig ; Makoto Sakai ; Shiori Kobayashi ; Michio Homma ; Masaaki Fujii ; Hideki Kandori ; Yuki Sudo
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：May 24, 2012
• 年：2012
• 卷：116
• 期：20
• 页码：5888-5899
• 全文大小：612K
• 年卷期：v.116,no.20(May 24, 2012)
• ISSN：1520-5207

文摘

Photoactive proteins with cognate chromophores are widespread in organisms, and function as light-energy converters or receptors for light-signal transduction. Rhodopsins, which have retinal (vitamin A aldehyde) as their chromophore within their seven transmembrane 伪-helices, are classified into two groups, microbial (type-1) and animal (type-2) rhodopsins. In general, light absorption by type-1 or type-2 rhodopsins triggers a trans鈥?i>cis or cis鈥?i>trans isomerization of the retinal, respectively, initiating their photochemical reactions. Recently, we found a new microbial rhodopsin (middle rhodopsin, MR), binding three types of retinal isomers in its original state: all-trans, 13-cis, and 11-cis. Here, we identified the absolute absorption spectra of MR by a combination of high performance liquid chromatography (HPLC) and UV鈥搗is spectroscopy under varying light conditions. The absorption maxima of MR with all-trans, 13-cis, or 11-cis retinal are located at 485, 479, and 495 nm, respectively. Their photocycles were analyzed by time-resolved laser spectroscopy using various laser wavelengths. In conclusion, we propose that the photocycles of MR are MR(trans) 鈫?MR_K:lifetime = 93 渭s 鈫?MR_M:lifetime = 12 ms 鈫?MR, MR(13-cis) 鈫?MR_O-like:lifetime = 5.1 ms 鈫?MR, and MR(11-cis) 鈫?MR_K-like:lifetime = 8.2 渭s 鈫?MR, respectively. Thus, we demonstrate that a single photoactive protein drives three independent photochemical reactions.