Menaquinone-7 in the reaction center complex of the green sulfur bacterium Chlorobium vibrioforme functions as the electron acceptor A1
Menaquinone-7 in the reaction center complex of the green sulfur bacterium Chlorobium vibrioforme functions as the electron acceptor A1
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DOI：
10.1021/bi973121t
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发表时间：
1998-03-10
期刊：
影响因子：
2.9
通讯作者：
Scheller, HV
中科院分区：
文献类型：
--
作者：
Kjær, B;Frigaard, NU;Scheller, HV
以绿色硫细菌Chlorobium vibrioforme NCIMB 8327为原料，制备了具有光合活性的反应中心复合物，并采用萃取-高效液相色谱法测定了复合物中醌类化合物的含量。分析显示1.7分子甲萘醌-7/反应中心的化学计量。在隔离的反应中心中没有检测到其他醌类，而膜制剂也含有氯醌。用电子顺磁共振（EPR）谱研究了醌类化合物参与电子传递的可能性。一个高度各向异性的自由基检测到的Q-带EPR光谱在两个膜和隔离的反应中心后，暗还原与连二亚硫酸钠和光积累在205 K。在34 GHz下，EPR谱的特征在于g张量，g（xx）= 2.0063，g（yy）= 2.0052，g（zz）= 2.0020，Δ B为0.7 mT，与其作为醌的鉴定一致。该光谱在g值和线宽方面与聚球藻7002的光系统I中的光累积A（1）（-）高度相似。结果表明，甲基萘醌-7在绿色硫细菌反应中心与光系统I中的叶绿醌类似。
Photosynthetically active reaction center complexes were prepared from the green sulfur bacterium Chlorobium vibrioforme NCIMB 8327, and the content of quinones was determined by extraction and high-performance liquid chromatography. The analysis showed a stoichiometry of 1.7 molecules of menaquinone-7/reaction center. No other quinones were detected in the isolated reaction centers, whereas membrane preparations also contained chlorobiumquinone. The possible involvement of quinones in electron transport was investigated by electron paramagnetic resonance (EPR) spectroscopy. A highly anisotropic radical was detected by Q-band EPR spectroscopy in both membranes and isolated reaction centers following dark reduction with sodium dithionite and photoaccumulation at 205 K. At 34 GHz, the EPR spectrum is characterized by a g tensor with g(xx) = 2.0063, g(yy) = 2.0052, g(zz) = 2.0020 and Delta B of 0.7 mT, consistent with its identification as a quinone. This spectrum is highly similar in terms of g values and line widths to photoaccumulated A(1)(-) in photosystem I of Synechococcus sp. PCC 7002. The results indicate that menaquinone-7 in the green sulfur bacterial reaction center is analogous to phylloquinone in photosystem I.