title: Directly probing redox-linked quinones in photosystem II membrane fragments via UV resonance Raman scattering.
abstract: 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.
authors: 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. Electronic address: junchen@dicp.ac.cn.
authors: Jun
authors: J
authors: Chen
authors: Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors: Mingdong
authors: M
authors: Yao
authors: School of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, United States.
authors: Cynthia V
authors: CV
authors: Pagba
authors: Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors: Yang
authors: Y
authors: Zheng
authors: Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors: Liping
authors: L
authors: Fei
authors: State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors: Zhaochi
authors: Z
authors: Feng
authors: School of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, United States.
authors: Bridgette A
authors: BA
authors: Barry
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry; D004579:Electron Transport; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D011809:Quinones / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman / Q000379:methods*; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism*; D014732:Vibration
chemical_list: D045332:Photosystem II Protein Complex; D011809:Quinones; D002734:Chlorophyll
keywords: Carbonyl bond; Electron transfer; Lipid membrane; Photosynthesis; Protein dynamics; Proton transfer