細菌視紫質受光激發後，其內部的視黃醛分子會進行光異構化反應，並驅動光迴圈反應進行質子傳遞並產生生物體所需的ATP。藉由奈米碟技術，單體化之細菌視紫質可被包覆於由膜支架蛋白及脂雙層所形成的脂質奈米碟中，透過調整脂雙層的脂質組成探討其對細菌視紫質性質之影響。為了進一步探討不同環境變因之影響，吾人亦將原生紫膜形式之細菌視紫質(PM)、包覆於界面活性劑TX-100內之單體化細菌視紫質(mbR_TX100)，以及利用界面活性劑CHAPS去除紫膜中部分脂質之細菌視紫質(dPM)納入實驗進行比較。本實驗利用飛秒瞬態吸收光譜測量細菌視紫質光迴圈反應中I state之生命期，並使用575 nm及550 nm兩種激發波長，以確認激發波長對光異構化反應之影響。根據實驗結果發現，575 nm及550 nm兩種激發波長下可以觀察到相似的光異構化速率，而三聚體形式之細菌視紫質具有相似之光異構化速率(I state生命期約0.6至0.7 ps)，且較單體形式細菌視紫質(I state生命期約0.9至1.4 ps)更快。在奈米碟細菌視紫質的實驗中則發現，使用單一脂質DOPG或DOPC組成之奈米碟細菌視紫質，不論脂質電性皆具有相似之光異構化速率，而使用DOPG及DOPC比例為1:1組成之奈米碟細菌視紫質則具有較慢之光異構化速率。吾人認為脂質環境改變會影響靜態吸收峰位置，而蛋白質結構及寡聚狀態改變可能會影響視黃醛分子周遭之電荷分布，導致光異構化速率產生變化。此外，吾人推論奈米碟中的脂質電性比例會影響光異構化反應，且在配合黃信毓之論文後得以進一步說明本研究所觀察到之趨勢。

Monomerized bacteriorhodopsin (mbR) was embedded in lipid nanodisc (nbR) using different lipid compositions. For comparison with varied oligomeric statuses of bR, native bR in purple membrane (PM), partially delipidated PM (dPM) and momeric bR solubilized in TX-100 (mbR) were also prepared. When bR is excited by light, the retinal of bR undergoes photoisomerization from all-trans, 15-anti to 13-cis, 15-anti via the excited state (called I state), then initiates a photocycle reaction. The lifetime of the excited state of all-trans, 15-anti (I state) was detected using femtosecond transient absorption upon excitation at 575 nm and 550 nm, to confirm the excitation wavelength dependent photoisomerization kinetics. We found that the bR in trimeric forms, including PM and dPM, possess similar retinal photoisomerization kinetics (lifetime of I state τ_I=0.6-0.7 ps), which is faster than in mbR and nbR (τ_I=0.9-1.4 ps). Moreover, there is no distinguishable difference in photoisomerization when monomeric bR was embedded in different lipid composition of dioleoyl phosphatidylglycerol (DOPG) and dioleoyl phosphatidylcholine (DOPC). However, when lipid nanodisc containing ratio of DOPG : DOPC = 1:1, we observed a slightly slower rate of photoisomerization. Besides, the retinal photoisomerization kinetics upon excitation at 575 nm and 550 nm behavior similarly. We thus suggest that the positions of the charged residues at the vicinity of retinal in the monomerized bR differ from those in the trimer form and thus altered the rate of photoisomerization.

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