Pathway of proton transfer in bacterial reaction centers: replacement of glutamic acid 212 in the L subunit by glutamine inhibits quinone (secondary acceptor) turnover.
Pathway of proton transfer in bacterial reaction centers: replacement of glutamic acid 212 in the L subunit by glutamine inhibits quinone (secondary acceptor) turnover.
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细菌反应中心质子转移途径：用谷氨酰胺取代L亚基中的谷氨酸212可抑制醌（次级受体）周转。
DOI：
10.1073/pnas.86.17.6602
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发表时间：
1989
影响因子：
11.1
通讯作者：
Okamura,MY
中科院分区：
文献类型：
--
作者：
Paddock,ML;Rongey,SH;Feher,G;Okamura,MY
采用定点诱变方法研究了球形红杆菌反应中心（RCs）中质子转移的机理。谷氨酰胺取代L亚基（位于二级受体（QB）结合位点附近的可质子化残基）的Glu-212，使细胞色素c到2,3-二甲氧基-5-甲基苯醌（UQ0）的体外电子周转率降低了25倍。电子向QB的传递速率基本保持不变。因此，可以假设突变体的周转减少是由于质子转移到QB2-的速率降低。突变体RC的正向电子转移速率DQA-QB----DQAQB-和反向反应速率D+QAQB- ----DQAQB（其中D =主要供体，QA =主要受体）缺乏pH依赖性，这表明在原生RC中观察到的pH依赖性是由于Glu-212，其pKa值异常高，为9.5 +/- 0.3。这些结果支持Glu-212作为质子供体参与还原QB。
The mechanism of proton transfer in the reaction centers (RCs) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Replacement of Glu-212 of the L subunit, a protonatable residue located near the secondary acceptor (QB) binding site, by glutamine reduced the in vitro electron turnover from cytochrome c to 2,3-dimethoxy-5-methylbenzoquinone (UQ0) by a factor of 25. The electron transfer rate to QB remained essentially unimpaired. Consequently, it is postulated that the reduced turnover in the mutant is due to a reduced rate of proton transfer to QB2-. The lack of pH dependence of the forward electron transfer rate DQA-QB----DQAQB- and the back reaction rate D+QAQB- ----DQAQB (where D = primary donor and QA = primary acceptor) in the mutant RC indicate that the observed pH dependence in the native RC is due to Glu-212, which has an anomalously high pKa value of 9.5 +/- 0.3. These results support the involvement of Glu-212 as a proton donor to reduced QB.