B850 complex

D. Method for Reconstitution of Carotenoids into the B850 Complex of Rb. sphaeroides R-26.1.242... 

Theiler R and Zuber H. The light-harvesting polypeptides of Rhodopseudomonas sphaeroides R-26-1. II. Conformational analyses by attenuated total reflection infrared spectroscopy and possible molecular structure of the hydrophobic domain of the B850 complex. Hoppe-Seyler s Z. Physiol. Chem. 1984 365 721-729. 

Kuhn, O., Sundstrom, V., Pullerits, T. Fluorescence depolarization dynamics in the B850 complex of purple bacteria. Chem. Phys. 275, 15-30 (2002)... 

Figure 23-26 (A), (B) Arrangement of bacteriochlorophyll chromophores in the cyclic LH2 array of Rhodopseudomonas acidophila. The B850 subunits are gray while the B800 subunits are black. (C) Fluorescence-excitation spectra. Top trace, for an ensemble of LH2 complexes, other traces, for several individual LH2 complexes at 1.2K. Fine structure is evident for the B800 but not for the B850 chromophores. From van Oijen et al.299 with permission.

Good spectroscopic data for well-defined complexes from purple bacteria are available (Refs. 28, 29 and references therein), but general agreement is lacking on what, if anything, constitutes a minimum complex. One candidate is the so-called photoreceptor unit , consisting of core antenna plus reaction center [30]. This cyclic unit structure has features in common with secondary-antenna cyclic structures [31]. Some exciton analyses apply to any of these membrane antennas, others are specific. A key issue is the explanation of spectral data on the B850 part of the... 

Figure 1. Schematic representation of the LH2 antenna complex from Rps. acidophila [7]. Only bacteriochlorophyll molecules are considered, for clarity. The squares represent bacteriochlorophyll molecules which lie in the plane of the page. Their assembly is called the B800 system (see text). The rectangles represent the BChl molecules which are perpendicular to the plane of the page. These latter are in almost a face-to-face arrangement and constitute the B850 system.

Figure 2. Schematization of the overall energy migration within the antenna network to reach the reaction center. The small and large wheels represent the LH2 and LHl complexes, respectively. For the LHl complex, only the B850 system is represented.

Fig. 26.1. Structure of the LH2 complex from Rps. acidophila as determined by X-ray diffraction. Part (a) shows the whole pigment-protein complex in a top view part (b) displays the spatial arrangement of the BChl a in a tilted side-view. The B800 BChl a pigments are shown in hght gray and the B850 BChl a molecules are shown in dark gray. The numbers indicate the centre to centre distances of the pigments in A. The arrows indicate the direction of the Qy transition moments. The phytol chains of the pigments are removed for clarity. Adapted from [3]...

J. Koepke, X. Hu, C. Muenke, K. Schulten, H. Michel, The crystal structure of the light harvesting complex II (B800-B850) from Rhodospirillum molischianum. Structure 4, 581-597 (1996)... 

C. Hofmann, T.J. Aartsma, J. Kohler, Energetic disorder and the B850-exciton states of individual light-harvesting 2 complexes from Rhodopseudomonas acidophila. Chem. Phys. Lett. 395, 373-378 (2004a)... 

M. Ketelaars, A.M. van Oijen, M. Matsushita, J. Kohler, J. Schmidt, T.J. Aartsma, Spectroscopy on the B850 band of individual hght-harvesting 2 complexes of Rhodopseudomonas acidophila I. Experiments and Monte-Carlo simulations. Biophys. J. 80, 1591-1603 (2001)... 

P-OG - octyl-P-glucopyranoside B - stands for h.ulk in, e.g., B850 to designate a lightharvesting BChl-protein complex B - monomeric bacteriochlorophyll /-cytochrome bj ... 

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