Chen Jun, Yao Mingdong, Pagba Cynthia V, Zheng Yang, Fei Liping, Feng Zhaochi, Barry Bridgette A
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Biochim Biophys Acta. 2015 Jun-Jul;1847(6-7):558-64. doi: 10.1016/j.bbabio.2015.03.002. Epub 2015 Mar 17.
In photosynthesis, photosystem II (PSII) harvests sunlight with bound pigments to oxidize water and reduce quinone to quinol, which serves as electron and proton mediators for solar-to-chemical energy conversion. At least two types of quinone cofactors in PSII are redox-linked: QA, and QB. Here, we for the first time apply 257-nm ultraviolet resonance Raman (UVRR) spectroscopy to acquire the molecular vibrations of plastoquinone (PQ) in PSII membranes. Owing to the resonance enhancement effect, the vibrational signal of PQ in PSII membranes is prominent. A strong band at 1661 cm(-1) is assigned to ring CC/CO symmetric stretch mode (ν8a mode) of PQ, and a weak band at 469 cm(-1) to ring stretch mode. By using a pump-probe difference UVRR method and a sample jet technique, the signals of QA and QB can be distinguished. A frequency difference of 1.4 cm(-1) in ν8a vibrational mode between QA and QB is observed, corresponding to ~86 mV redox potential difference imposed by their protein environment. In addition, there are other PQs in the PSII membranes. A negligible anharmonicity effect on their combination band at 2130 cm(-1) suggests that the 'other PQs' are situated in a hydrophobic environment. The detection of the 'other PQs' might be consistent with the view that another functional PQ cofactor (not QA or QB) exists in PSII. This UVRR approach will be useful to the study of quinone molecules in photosynthesis or other biological systems.
在光合作用中，光系统II（PSII）利用结合的色素捕获阳光，以氧化水并将醌还原为醌醇，醌醇作为电子和质子介质用于太阳能到化学能的转换。PSII中至少有两种醌辅因子是氧化还原连接的：QA和QB。在此，我们首次应用257纳米紫外共振拉曼（UVRR）光谱来获取PSII膜中质体醌（PQ）的分子振动。由于共振增强效应，PSII膜中PQ的振动信号很突出。在1661厘米-1处的强带归属于PQ的环CC/CO对称拉伸模式（ν8a模式），在469厘米-1处的弱带归属于环拉伸模式。通过使用泵浦-探测差分UVRR方法和样品喷射技术，可以区分QA和QB的信号。观察到QA和QB在ν8a振动模式下的频率差为1.4厘米-1，这对应于它们的蛋白质环境施加的约86毫伏氧化还原电位差。此外，PSII膜中还有其他PQ。对其在2130厘米-1处的组合带的非谐效应可忽略不计，这表明“其他PQ”位于疏水环境中。检测到“其他PQ”可能与PSII中存在另一种功能性PQ辅因子（不是QA或QB）的观点一致。这种UVRR方法将有助于研究光合作用或其他生物系统中的醌分子。
