Functions of lipophilic quinones in photosynthetic reaction sytems of photosynthesis

亲脂性醌在光合作用反应体系中的作用

基本信息

批准号：
61480009
负责人：
KATOH Sakae
金额：
$ 4.22万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

Functions of plastoquinone associated with PS II Preparations isolated from the thermophilic cyanobacterium Sybechococcus sp. were studied1. Photoaffinty labeling of various PS II preparations clearly demonstrated for the first time that a phenol-type herbicide binds to the 28 KDa Q_B-protein and the 47 KDa chlorophyll-carrying protein has a plastoquinone binding site2. Numbers and functions pf plastoquinone molecules associated with PS II preparetions were determined. Three quinone molecules present in the oxygen evolving preparations function as Q_A and Q_G and possibly on the water side of the reaction center of PS II3. Chemical composition of the highly purified oxygen evolving comolexes was analyzed. The results show that two plastoquinone molecules, which function as Q_A and on the water side of PS II,are needed for oxygen evolution4. A unigue mode of benzoquinone reduction was found in the oxygen evolving prepqrations. High rate of oxygen evolution was obtained with lipophilic benzoquinones, while less lipophilic molecules were poor electron acceptors. DCMU strongly inhibited reduction of all the electron acceptors examined. In contrast, DBMIB suppressed competitively reduction of benzoquinones but not that of ferricyanide and dichlorophenolindophenol. This suggests that benzoquinones bind to the Q_B-site, by replacing plastoquinone, and accept electrons directly from Q_A. The arrhenius plot of benzoquinone reduction suggests that a change in the conformation of the Q_B-protein occurs at 19゜C5. Duroquinol oxidation by PS I in the cyanobacterial cells was also inhibited competitively by DBMIB, suggesting a common inhibition mechanism of DBMIB between the ozygen evolving complexes and the cytochrome b_6-f complexes.

研究了从嗜热蓝细菌 Sybechococcus sp 中分离出来的 PS II 制剂的质体醌的功能，首次清楚地证明了苯酚型除草剂与 28 KDa Q_B 蛋白和 47 KDa 结合。叶绿素携带蛋白具有质体醌结合位点2。确定了与 PS II 制剂相关的三个醌分子，其功能为 Q_A 和 Q_G，并且可能位于 PS II3 反应中心的水侧。结果表明，在PS II的水侧起Q_A作用的两个质体醌分子是析氧所必需的4。亲脂性苯醌的放氧速率较高，而亲脂性较低的分子是较差的电子受体，相反，DBMIB 会抑制苯醌的竞争性还原，但不会抑制铁氰化物和铁氰化物的还原。这表明苯醌通过取代质体醌与 Q_B 位点结合并接受电子。直接来自 Q_A。苯醌还原的阿伦尼乌斯图表明，蓝藻细胞中 PS I 引起的 Q_B 蛋白构象变化也被 DBMIB 竞争性抑制，这表明了 DBMIB 的共同抑制机制。 DBMIB 位于产氧复合物和细胞色素 b_6-f 复合物之间。