Electron transfer , photosynthetic reaction

C Lautwasser, U Finkele, H Scheer and WZinth (1991) Temperature dependence of the primary electron transfers photosynthetic reaction centers from Rhodobacter sphaeroides. Chem Phys Lett 183 471-477... 

Breton J, Martin J-L, Fleming G R and Lambry J-C 1988 Low-temperature femtosecond spectroscopy of the initial step of electron transfer in reaction centers from photosynthetic purple bacteria Biochemistry 27 8276... 

Likhtenshtein, G.I. (1996a) Role of orbital and dynamic factors in electron transfer in reaction centers of photosynthetic systems. J. Phochem. Photobiol. A Chem. 96, 79-92. 

Zinth, W., and Kaiser, W., 1993, Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. In The Photosynthetic Reaction Center, (J. Deisenhofer and J. R. Norris, eds.) Volume 2, 71988, Academic Press, San Diego, USA. 

Proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of chemical and biological processes. For example, PCET is required for the conversion of energy in photosynthesis [1] and respiration [2], In particular, the coupling between proton motion and electron transfer is involved in the pumping of protons across biological membranes in photosynthetic reaction centers [1] and in the conduction of electrons in cytochrome c [3]. In addition to biological processes, PCET is also important in electrochemical processes [4, 5] and in solid state materials [6]. 

YD Halsey and WW Parson (1974) Identification of ubiquinone as the secondary electron acceptor in the photosynthetic apparatus of Chromatium vinosum. Biochim Biophys Acta 347 404-416 A Vermeglio (1977) Secondary electron transfer in reaction centers of Rhodopseudomonas sphaeroldes. Out-of-phase periodicity of two for the formation of ubisemiquinone and fully reduced ubiquinone. Biochim Biophys Acta. 459 516-524... 

Fig. 9. (A) Absorption spectrum of Rb. sphaeroides used as a reference to show the Qx and Qy bands of the primary donor (P), BChl [B] and bacteriopheophytin [BO] (B) Femtosecond absorption changes at 920 (a), 785 (b) and 545 nm (c) vs. the delay time of the monitoring pulse measured at room temperature, and (C) absorption changes at 920 (a) and 794 nm (b) measured at 25 K. Figure source (A) see Fig. 7 (B) Holzapfel, Finkele, Kaiser, Oesterheldt, Scheer, Stilz and Zinth (1990) Initial electron transferin the reaction center from Rhodobacter sphaeroides. Proc Nat Acad Sci, USA 87 5170 (C) Zinth and Kaiser (1993) Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. I n JR Norris and J Deisenhofer (eds) The Photosynthetic Reaction Center, Voi il, p 82. Acad Press.

Tiede DM, Budil DE, Tang J et al. Symmetry breaking structures involved in the docking of cytochrome c and primary electron transfer in reaction centers of rhodobacter sphaeroides. In Breton J, Vermeglio A, eds. The Photosynthetic Bacterial Reaction Center, Structure and Dynamics. New York Plenum, 1988 13-20. 

J. Jortner and M.E. Michel-Beyerle, Some Asp>ects of Energy Transfer in Antennas and Electron Transfer in Reaction Centers of Photosynthetic Bacteria, in "Antennas and Reaction Centers of Photosynthetic Bacteria", M.E. Michel-Beyerle, ed., Springer-Verlag, Berlin (1985). 

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

Boxer S G, Goldstein R A, Lockhart D J, Middendorf T R and Takiff L 1989 Excited states, electron-transfer reactions, and intermediates in bacterial photosynthetic reaction centers J. Rhys. Chem. 93 8280-94... 

Both PSI and PSII are necessary for photosynthesis, but the systems do not operate in the implied temporal sequence. There is also considerable pooling of electrons in intermediates between the two photosystems, and the indicated photoacts seldom occur in unison. The terms PSI and PSII have come to represent two distinct, but interacting reaction centers in photosynthetic membranes (36,37) the two centers are considered in combination with the proteins and electron-transfer processes specific to the separate centers. 

M Marchi, IN Gehlen, D Chandler, M Newton. Diabatic surfaces and the pathway for primary electron transfer in a photosynthetic reaction center. 1 Am Chem Soc 115 4178-4190, 1993. 

Figure 12.15 Schematic arrangement of the photosynthetic pigments in the reaction center of Rhodopseudomonas viridis. The twofold symmetry axis that relates the L and the M subunits is aligned vertically in the plane of the paper. Electron transfer proceeds preferentially along the branch to the right. The periplasmic side of the membrane is near the top, and the cytoplasmic side is near the bottom of the structure. (From B. Furugren, courtesy of the Royal Swedish Academy of Science.)...

What molecular architecture couples the absorption of light energy to rapid electron-transfer events, in turn coupling these e transfers to proton translocations so that ATP synthesis is possible Part of the answer to this question lies in the membrane-associated nature of the photosystems. Membrane proteins have been difficult to study due to their insolubility in the usual aqueous solvents employed in protein biochemistry. A major breakthrough occurred in 1984 when Johann Deisenhofer, Hartmut Michel, and Robert Huber reported the first X-ray crystallographic analysis of a membrane protein. To the great benefit of photosynthesis research, this protein was the reaction center from the photosynthetic purple bacterium Rhodopseudomonas viridis. This research earned these three scientists the 1984 Nobel Prize in chemistry. 

Photosynthetic Electron Transfer in the R. viridis Reaction Center... 

Willner, I and Willner, B. Artifical Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218... 

Studies (see, e.g., (101)) indicate that photosynthesis originated after the development of respiratory electron transfer pathways (99, 143). The photosynthetic reaction center, in this scenario, would have been created in order to enhance the efficiency of the already existing electron transport chains, that is, by adding a light-driven cycle around the cytochrome be complex. The Rieske protein as the key subunit in cytochrome be complexes would in this picture have contributed the first iron-sulfur center involved in photosynthetic mechanisms (since on the basis of the present data, it seems likely to us that the first photosynthetic RC resembled RCII, i.e., was devoid of iron—sulfur clusters). 

It is interesting to compare the thermal-treatment effect on the secondary structure of two proteins, namely, bacteriorhodopsin (BR) and photosynthetic reaction centers from Rhodopseudomonas viridis (RC). The investigation was done for three types of samples for each object-solution, LB film, and self-assembled film. Both proteins are membrane ones and are objects of numerous studies, for they play a key role in photosynthesis, providing a light-induced charge transfer through membranes—electrons in the case of RC and protons in the case of BR. 

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