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Author Iwaki, Masayo ♦ Itoh, Shigeru ♦ Kumazaki, Shigeichi ♦ Yoshihara, Keitaro ♦ Erabi, Tatsuo
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ PHYSICS ♦ CHLOROPHYLL ♦ ELECTRON TRANSFER ♦ QUINONES ♦ PHOTOCHEMICAL REACTIONS ♦ PHOTOSYNTHETIC REACTION CENTERS ♦ PLANTS ♦ CHEMICAL REACTION KINETICS ♦ ELECTRON-ELECTRON COUPLING ♦ ENERGY LEVELS ♦ MOLECULAR STRUCTURE
Abstract The rate of the electron transfer reaction from the reduced primary electron acceptor chlorophyll a (A{sub 0}{sup -}) to the secondary acceptor quinone (Q) was measured by picosecond-nanosecond laser spectroscopy at 280 K in the photosynthetic reaction center (RC) complex of plant photosystem I (PS I). The free energy change ({Delta}G{sub 0}) of the reaction was varied between -1.1 and +0.2 eV by the reconstitution of 13 different quinone/quinonoid compounds after the extraction of the intrinsic phylloquinone. Phylloquinone and its natural analog menaquinone, both of which show a {Delta}G{sup 0} value of -0.34 eV, gave the highest rate constant (k) of (23 ps){sup -1}. Analysis of log k versus {Delta}G{sup 0} plot according to the quantum mechanical electron transfer theory gave the total reorganization energy ({lambda}{sub total}) of 0.30 eV and the electronic coupling (V) of 14 cm{sup -1}. The natural system is shown to be highly optimized to give a {Delta}G{sup 0} = -{lambda}{sub total} condition. The {lambda}{sub total} value is smaller and the V value is larger than those estimated in the corresponding reaction between the reduced primary acceptor bacteriopheophytin (H{sup -}) and the secondary acceptor ubiquinone (Q{sub A}) in the purple bacterial RC complex. It is concluded that the A{sub 0}{sup -}Q {yields} A{sub 0}Q{sup -} reaction in the PS I RC occurs in protein environments, which give a low dielectric property, with a shorter electron transfer distance compared to the reaction between H and Q{sub A}. 46 refs., 7 figs., 2 tabs.
ISSN 00223654
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-06-20
Publisher Place United States
Journal Journal of Physical Chemistry
Volume Number 100
Issue Number 25


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