Photosynthesis Bacterial Reaction Center

Loach, P.A. (1980) Bacterial reaction center (RC) and photoacceptor complex preparations, in San-Pietro, A. (ed) Methods in Enzymology, Vol. 69, Photosynthesis and Nitrogen Fixation, part C, Academic Press, N.Y. pp. 155-172. 

Sporlein, S., Zinth, W., Meyer, M., Scheer, H., and Wachtveitl, J. (2000) Primary electron transfer in modified bacterial reaction centers optimization of the first events in photosynthesis, Chem. Phys. Lett. 322(6), 454-464. 

As indicated in Figure I, wild-type bacterial reaction centers also contain a carotenoid polyene. This polyene is not involved as a donor or acceptor in the normal electron transfer sequence, although carotenoid radical cations have been observed spectroscopically in photosynthetic preparations under certain conditions [18,19]. In many of the artificial photosynthetic systems which will be discussed below, the carotenoid is used as a convenient secondary electron donor. Carotenoids do perform two important functions in photosynthesis. They provide photoprotection from singlet oxygen damage, and act as light-gathering antennas for the special pair (see Sections III and IV). 

LNM Duysens (1952) Transfer of excitation energy in photosynthesis. Utrecht University dissertation RK Ciayton (1965) The biophysical problems of photosynthesis. Science 149 1246-1254 WW Parson (1978) The bacterial reaction center, in J Amesz (ed) Photosynthesis, pp 43-61. Eisevier R4. G Feher (1992) Identification and characterization of the primary donor in bacterial photosynthesis a chronological account of an EPR/ENDOR Investigation (The Bruker Lecture). J Chem Soc Perkin Transactions 2 1861-1874... 

Fig. 3. Absorbance-change patterns due to quinone reaction in the bacterial reaction center of Rb. sphaeroides excited by four consecutive flashes. Quinone compositions examined were (A) only Qa present (B) only Qa and Qb present (C) Qa, Qb and quinone pool all present. Figure adapted from Clayton (1980) Photosynthesis Physical Mechanisms and Chemical Patterns, pp 215, 216. Cambridge University Press.

R1. WW Parson (1987) The bacterial reaction center. In J Amesz (ed) Photosynthesis, pp 43-61. Elsevier... 

Fig. 3. Top row formulation of the reaction sequence involved In the photochemical charge separation of the photosynthetic bacterial reaction center. (D is the excitation and charge separation. the electron transfer to the (secondary) acceptors, and the electron donation by a secondary donor, the cytochrome, to the photooxidized primary donor P. Figure adapted from RK Clayton (1980) Photosynthesis. Physical Mechanism and Chemical Patterns, p 91. Cambridge Univ Press.

As seen earlier in Chapter 2 on bacterial reaction centers, crystallization of the reaction-center protein of the photosynthetic h iCttn xm Rhodopseudomonas viridis by Michel in 1982 and subsequent determination ofthe three-dimensional structure ofthe reaction center by Deisenhofer, Epp, Miki, Huber and Michel in 1984 led to tremendous advances in the understanding ofthe structure-function relationship in bacterial photosynthesis. Furthermore, because of certain similarities between the photochemical behavior of the components of some photosynthetic bacteria and that of photosystem II, research in photosystem-II was greatly stimulated to its benefit by these advances. In this way, it became obvious that the ability to prepare crystals from the reaction-center complexes of photosystems I and II would be of great importance. However, it was also recognized that, compared with the bacterial reaction center, the PS-I reaction center is more complex, consisting of many more protein subunits and electron carriers, not to mention the greater number of core-antenna chlorophyll molecules. 

Fig. 2. (A) K-band ESP-EPR spectra of the CPI complex (top) and Rb sphaeroides R26 reaction-center complex (bottom) in the charge-separated states [P700 -A,4 and [P870 Q4, respectively (B) X-band ESP-EPR spectra of spinach PS-I particles extracted with a hexane-MeOH mixture (a), reconstituted with protonated (b) and deuterated (c) vitamin Ki (C) ESP-EPR spectra of spinach PS-I particle in glycine buffer at pH 10.8 and untreated (a), reduced with 50 mM dithionite and 0,5 mM methyl viologen and dark-incubated (b), and the reduced sample dialyzed overnight against glycine buffer and reconcentrated (c). Figure source (A) Petersen, Stehlik, Gast and Thurnauer (1987) Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR evidence that the photosystem I acceptor is a quinone. Photosynthesis Res 14 22 (B) and (C) Snyder and Thurnauer (1993) Electron spin polarization in photosynthetic reaction centers. In J Deisenhofer and JR Norris (eds) The Photosynthetic Reaction Center, Vol 11 313,315.

J Petersen, D Stehlik, P Gast and MC Thurnauer (1987) Comparison of the electron spin polarized spectrum found in piant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR Evidence that the photosystem I acceptoris a quinone. Photosynthesis Res 14 15-29... 

In this paper we give an account of our ongoing effort to understand bacterial photosynthesis at the atomic level. First, we describe earlier simulations which investigate the nuclear motion coupled to the primary donor excitation in bacterial reaction centers (RC). Then, we discuss the molecular modeling of the chromophores of the RC of rhodohacter sphaeroides. Finally, we report on our latest molecular dynamics simulation results concerning a RC in a detergent micelle. 

Frank HA (1992) Electron paramagnetic resonance studies of carotenoids. Meth Enzymol 213 305-312 Erank HA (1993) Carotenoids in photosynthetic bacterial reaction centers Structure, spectroscopy, and photochemistry. In Deisenhofer J andNorris JR(eds) The Photosynthetic Reaction Center, Vol II, pp 221-237. Academic Press, San Diego Prank HA and CogdeU RJ (1996) Carotenoids in Photosynthesis. Photochem Photobiol 63 257-264... 

Contributions in Chem. Phys. 197,223-472 (19995), Special issue on Photosynthesis and die Bacterial Reaction Center. 

In photosynthesis, the primary charge separation occurs in the reaction center. To study this electron transfer chain, magnetic resonance measurements are carried out on bacterial reaction centers of Rhodobacter sphaeroides R 26. The investigated triplet states are used as intrinsic probes of the pigment interactions in this protein complex. 

Oxygenic photosynthesis takes place in two photochemical reaction centers Photosystem I (PSI) and Photosystem II (PSII). While PSn is believed to be closely related to the reaction center of purple bacteria (1), PSI spears to be unique to oxygenic photosynthetic organisms. It is clear that this photosynthetic complex has no structural or functional similarities to the bacterial reaction center, nevertheless it plays a major role in the oxygenic photosynthetic process. Its function in the reducing site of the electron transfer chain enables the reduction of ferredoxin, and eventually the reduction of one of the energy components formed in the process, NADPH. 

M. Plato, F. Lendzian, W. Lubitz, E. Trankle, K. Mdbius, in The Photosynthetic Bacterial Reaction Center, Eds. J. Breton, A. Vermeglio (Plenum Press, New York, 1988) pp. 379-388 M. Plato, K. Mobius, W. Lubitz, J.P. Allen, G. Feher, in Perspectives of Photosynthesis (Kluwer, The Netherlands, 1990) pp. 423-434 D. Bumann Diploma thesis. Free University of Berlin (Berlin,... 

Substantiation of these points must await quantitative analyses of both frequency displacements and relative band intensities in RR spectra, but these results do clearly show that even 10 nJ excitation in a 30 ps pulse alters can generate photo-reduction of the Bpheo in reaction centers and that these changes can be observed by RR scattering. These results thereby suggest that RR spectroscopy can make important contributions to an understanding of the structural dynamics underlying the primary events of photosynthesis in bacterial reaction centers. 

The existence of the "special pair" (SP) of bacteriochlorophylls(BChl) was postulated nearly 20 years ago to describe the structural organization of the primary electron donor (P) of bacterial photosynthesis. The SP hypothesis was proposed based on magnetic resonance data measured for the oxidized radical cation of P in the bacterial reaction center (RC) protein (1,2). The SP concept was validated when detailed crystallographic data became available for the RCs from Rhodopseiidomonas viridis and Rhodobacter sphaeroides (3-71. We now know that two strongly-interacting BChls with local C2 symmetry constitute the primary electron donor. Moreover, two monomeric BChls and two bacteriopheophytins (BPh) are related to each other about the same symmetry element. This structure reveals two prosthetic group chains, the L and M branches, that span the membrane. 

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