Selective immobilization of bacterial light-harvesting proteins and their photoelectric responses
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Research Letter
Selective immobilization of bacterial light-harvesting proteins and their photoelectric responses Rei Furukawa, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu, Tokyo 182-8585, Japan Masaharu Kondo, Shunsuke Yajima, and Kaori Harada, Nagoya Institute of Technology, Gokiso-cho, Nagoya, Aichi 466-8555, Japan Kenji V.P. Nagashima, Kanagawa University, Tsuchiya 2946, Hiratsuka, Kanagawa 259-1293, Japan Morio Nagata, Tokyo University of Science, 12-1 Ichigayafunagawara-cho, Shinjuku-ku, Tokyo 162-0826, Japan Kouji Iida, Nagoya Municipal Industrial Research Institute, Atsuta-ku, Nagoya 456-0058, Japan Takehisa Dewa, Nagoya Institute of Technology, Gokiso-cho, Nagoya, Aichi 466-8555, Japan Mamoru Nango, Nagoya Institute of Technology, Gokiso-cho, Nagoya, Aichi 466-8555, Japan; OCARINA, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan Address all correspondence to Rei Furukawa at [email protected] (Received 30 May 2018; accepted 3 August 2018)
Abstract With the aim of understanding the excitation energy transfer mechanism in natural photosynthetic membranes, light-harvesting (LH)2 and LH1-reaction center, which are pigment-protein complexes separated from Rhodobacter sphaeroides, were aligned on a planar electrode surface in stripe patterns at 5 µm intervals. Observation of the absorption spectrum and fluorescence microphotographs revealed selective immobilization and conservation of the pigments. Photocurrent signals were obtained when the electrode was illuminated at either 880 or 800 nm. The fabricated structure was confirmed to function as a natural photosynthetic membrane with the highest photocurrent signal being obtained when using a co-immobilized substrate under excitation at 800 nm.
Introduction Studies from multiple perspectives have agreed that photosynthesis, which is an energy-harvesting process in the life of plants and certain bacteria, is understood to convert solar energy extremely efficiently, with high quantum efficiency.[1] While the process initiates with photo-absorption by antenna pigments and ends with the synthesis of adenosine triphosphate via multiple energy/electron transfer processes, one photon is capable of deriving one electron. The structure and alignment of the pigment-protein complex are designed to enable this highly efficient flow. The proton pump system in purple bacteria is made from light-harvesting (LH) 1, 2 complexes, a reaction center (RC), and a cytochrome bc1 complex. The structures and the energy flow within this system have been described in the literature.[1] The organization of bacteriochlorophyll a (BChl a) in the complex gives the antenna pigments the capability to absorb different wavelengths. In the first step of the photosynthesis process, antenna pigments such as B800, B850 and B880 absorb solar energy. Excitation energy transfer (EET) then occurs in each pigment, from a lower energy level to a higher level, which finally excites the special pair (SP) that is located within the RC. The excitation energy is the
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