苯(酉昆)類在N,N-二甲基乙醯胺溶液中的光磷酸化作用

Formation of ATP by Photochemical Excitation of Benzoquinones in N,N-Dimethylacetamide Solution

李鴻文(Hung-Wen Lee)

指導教授 ： 黃坤博

中原大學/理學院/化學研究所/博士(2002年)

https://doi.org/10.6840/cycu200200438

摘要

摘 要
本篇論文的主要目的是探討在N,N—二甲基乙醯胺(N,N-dimethylacetamide)這種非水溶液中加入對苯(酉昆)類(p-benzoquinones)、ADP and Pi所組成的反應系統，進行一種新的光化學磷酸化反應途徑。
本實驗在有氧或無氧的條件下將不同數目的取代基(甲基)之對苯(酉昆)類反應系統分別照射日光或人造光源。結果顯示有0~3個甲基的對苯(酉昆)類均有ATP被合成。但是四甲基對苯(酉昆)(duroquinone)只有在很強的日光或人造紫外光源之下，才會有微量ATP產生。
推究其中可能原因為：由於四甲基對苯在2、3、5、6的四個甲基造成推電子效應，使得四甲基對苯(酉昆)之羰基(carbonyl group)上π-orbital 的能階上升。使得其最低三重激發態變為 3(π—π*)而不是1(n—π*)。由於處於3(π—π*)能階之羰基的氧化性不大，因此無法提供足夠的氧化力使ADP and Pi結合成ATP。如有氧氣存在，由於氧在各種對苯(酉昆)類系統中經由光刺激引發而會產生單態氧(single oxygen)、氫氧自由基(hydroxyl radical) …… 強氧化劑，這些強氧化劑是不利於本實驗系統中ATP的形成。
為了驗證上述的想法，本實驗加入諸如naphthalene、anthracene、hydroquinone、2,5—二甲基芙喃(2,5-dimethyl-furan)、水及重水(D2O)等各種物理或化學的消光劑(quencher) 。其中，不論有氧或是無氧的條件之下anthracene、水及重水的加入均使得ATP產量下降，但是在有氧條件下2,5—二甲基芙喃卻會使得ATP產量上升。
另一方面，有四甲基對苯(酉昆)之反應系統中，ATP不但不會產生，反而會受到四甲基對苯(酉昆)之高能激發態的破壞。當 anthracene或2,5—二甲基芙喃加入於四甲基對苯(酉昆)反應系統消除其高能激發態，則ATP的減少量會趨於緩和，甚至於會有微量ATP產生。
經由本實驗，作者相信這種新的光化學磷酸化作用是由對苯(酉昆)類經由光引發產生之高能激發態的最低三重態(lowest triplet state) 所引發。

關鍵字

對苯(酉昆) ； 消光劑A ； 光化學

並列摘要

A novel photophosphorylation reaction in a non-aqueous medium such as N,N-dimethylacetamide containing a p-benzoquinone, ADP and Pi was studied.
Several p-benzoquinones with various numbers of methyl groups were examined for their ATP formation ability upon exposure to daylight or other light sources, in the presence or absence of oxygen. The results indicated that ATP formation was easily observed for p-benzoquinones with zero to three methyl groups. In contrast, only trace amount of ATP was formed when duroquinone was irradiated with daylight or ultraviolet of high intensity.
Four methyl groups in duroquinone may exert electron-donating effect on the ring, which in the turn, may raise the π-molecular energy level in carbonyl group of duroquinone. Thus the lowest excited triplet state of carbonyl group may therefore become 3(π—π*) but not the original 3(n—π*) duroquinone exhibited in other quinones. The oxidizing power of 3(π—π*) excited carbonyl group in duroquinone might not be sufficient to induce ADP and Pi in generating ATP.
In the presence of oxygen and a light source, media containing quinones produce strong oxidant such as single oxygen and hydroxyl radical, which are not favored for the over-all ATP formation, probably by attacking the reactants themselves or the product, ATP. In order to prove this point, the effect of several physical or chemical quncher such as naphthalene、anthracene、hydroquinone、2.5-dimethylfuran, and water were examined. No matter in the absence or presence of oxygen, the yields of ATP formation in general were decreased when anthracene, H2OorD2O was added to the reaction system. However, the ATP formation was increased when 2.5-dimethylfuran was added in the presence of oxygen.
On the other hand, in the duroquinone reaction system, ATP formation was not detected under irradiation with a light source with λ>400nm. The existing ATP was even partially destroyed by photo-excited duroquinone. When anthraceneor 2.5-dimethylfuran were added to reaction system the tendency of ATP destruction was compromised, and trace amount of ATP could even be detected.
Taken together, we believe that this novel photochemical phosphorylation is induced by lowest triplet state 3(n—π*), a high-energy excited state triggered by light energy.

並列關鍵字

quinone ； ADP ； photochemistry ； ATP

參考文獻

1. S. Patai(Ed), The Chemistry of the Quinonoid Compounds 1988. Wiley Interscience, New York.

2. W. Herre, P. Weis, Spetrochim, Acta, 1973, 29, 203.

3. D. R. Kemp, G. Porter, Proc. R. Soc. London, Ser. A, 1971, 326, 117.

4. R. K. Asundi, R. S. Singh, Nature, 1955, 176, 1223.

5. T. Anno, A. Sado, J. Chem. Phys. 1960, 32, 1602.