Photosynthetic bacteria model

DOM is derived from autochthonous sources such as phytoplankton and photosynthetic bacteria (16) at Big Soda Lake near Fallon, Nevada. This lake is alkaline (pH 9.7) and chemically stratified. It contains DOC concentrations as high as 60 mg/L and dissolved salt concentrations as high as 88,000 mg/ L (17). The DOM in this lake is colorless. The fulvic acid fraction was isolated by adsorption chromatography (Amberlite XAD-8 resin) (18) and by zeo-trophic distillation of water from N,N-dimethylformamide (19). Average molecular model synthesis was achieved in a manner similar to that used for fulvic acid from the Suwannee River. The characterization data are presented in Table I and the structural model is presented in Structure 2. 

In the mid-1980s, Deisenhofer reported his model for the structure of photosystem II for two species of purple photosynthetic bacteria (Rho-dopseudomonas viridis and Rhodobacter) based on X-ray crystallography of... 

We now summarize in Fig. 11 the reaction-center structure and the known electron-transport reactions in purple bacteria. A simplified representation of the reaction-center and the light-harvesting complexes contained in the bacterial membrane is shown in Fig. 11 (A), followed by a column model and a cofactor model in Fig. 11 (B). The cofactor model is used to illustrate the various electron-transport steps with the associated rate constants in Fig. 11 (C), where the cofactors in the starting state (oxidized or reduced) are shown in solid black. When a cofactor first becomes reduced or oxidized, it is shown as an open symbol. We will also use this cofactor model and reaction sequence as a framework for introducing the remaining chapters throughout the section on photosynthetic bacteria. 

Fig. 6. Photochemical cycles showing coupling of electron transfer to proton transfer, cytochrome oxidation and quinone exchange in (A) native reaction centers where two Cyt c are oxidized in the cycie, (B) reaction centers where uptake of the first proton is inhibited, and (C) reaction centers where uptake ofthe second proton is inhibited (shading indicates the quinone pool). Figure source (A) Paddock, Rongey, McPherson, Juth, Feher and Okamura (1994) Pathway of proton transfer in bacterial reaction centers role of aspartate-L21Z in proton transfers associated with reduction of quinone to dihydroquinone. Biochemistry 33 734 (B) Okamura and Feher (1992) Proton transfer in reaction centers from photosynthetic bacteria. Annu Rev Biochemistry. 61 868 (C) Feher, Paddock, Rongey and Okamura (1992) Proton transfer pathways in photosynthetic reaction centers studied by site-directed mutagenesis. In A Pullman, J Jortner and B Pullman (eds) Membrane Proteins Structures, Interactions and Models, p 485. Kluwer.

Femtosecond kinetics of photochemical charge separation in photosynthetic bacteria at low temperatures (25 K) was studied by Lautwasser, Finkele, Scheer and Zinth using Rb. sphaeroides RCs depleted of quinones. Fig. 9 (C, a) shows the initial formation of P at 920 nm followed by a very rapid relaxation with a Ti of 1.4 0.3 ps. At 794 nm and 25 K, the absorption increases very rapidly to a maximum in about 0.1 and then decays to a minimum at tD 0.5 ps. This is followed by a slow rise and a plateau after 5 ps. The early rapid-decay component with a time constant of 0.3 0.15 ps appears to be the counterpart of the 0.9-ps component at room temperature. The data points in Fig. 9 (C, b) can be fitted by a model with three time constants, namely 0.3ps, l.Aps and 1 ns. 

Fig. 2. Model forthe chlorosome in Chloroflexus aurantiacus. Model adapted from Mimuro, Hirota, Nishimura, Moriyama, Yamazaki, Shimada, and Matsuura (1994) Molecular organization of bacteriochlorophylls in chlorosomes of the green photosynthetic bacteria Chloroflexus aurantiacus Studies of fluorescence depolarization accompanied with the energy transfer process. Photosynthesis Res. 41 190.

Fig. 5. Absorption (solid-line), the 900-nm fluorescence excitation (dotted-line) and fluorescence emission (dashed-line, excited at 715 nm) spectra of whole cells of Cf. aurantiacus. Figure source Blankenship, Brune and Wittmershaus (1988) Chlorosome antennas In green photosynthetic bacteria. In SE Stevens, Jr and DA Bryant (eds) Light-Energy Transduction in Photosynthesis Higher Plants and Bacterial Models, p 41. The American Society of Plant Physiologists.

KM Smith, LA Kehres and J Fajer (1983) Aggregation of the bacteriochlorophylls c, d and e. Models for the antenna chlorophylls of green and brown photosynthetic bacteria. J Am Chem Soc 105 1387-1389... 

DC Brune, T Nozawa and RE Blankenship (1987) Antenna organization in green photosynthetic bacteria. I. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes. Biochemistry 26 8644-8652... 

M Lutz and G van Brakal (1988) Ground state molecular interactions of bacteriochlorophyll c in chlorosomes of green bacteria and in model systems a resonance Raman study. In JM Olson, JG Omerod, J Amesz, E Stackenbrandt and HG Trper (eds) Green Photosynthetic Bacteria, pp 23-33. Plenum Press... 

The INDO/S model is in wide use today by many groups. The largest calculations of spectra that we are aware of to date are on the reaction center in photosynthetic bacteria, a system of 518 atoms and 1400 orbitals. ... 

Carotenoids function in photosynthetic reaction centers (RC) as triplet quenchers of the primary donor chlorophyll or bacteriochlorophyll triplet states. The best studied RCs are those of purple photosynthetic bacteria where atomic models are available based on X-ray crystallography and optical as well as magnetic resonance spectroscopies have yielded a detailed picture of the flow of triplet energy transfer. Good reviews of these topics can be found in (Frank, 1992, 1993 Frank and Cogdell, 1996). 

Over the past thirty years, numerous workers have been studying the chlorophyll molecule and its derivatives in vitro. From these studies excellent models for the photoactive chlorophyll in green plants and photosynthetic bacteria have evolved. Most of the in vitro studies have involved comparisons between static properties of the chlorophylls in vitro and the chlorophylls in vivo however, recently a number of groups have begun to probe the dynamics of some of the models for the photoactive chlorophyll found in the reaction center. Excellent reviews of primary events in photosynthetic bacteria and green plants can be found in Ref. 1, 2, and 9. Therefore, the details will only be briefly reviewed in the next section. The extensive work by Katz and co-workers on the in vitro properties of chlorophyll laid the foundation for all of the model systems that have been proposed so far. Since the early work of Katz s group has also been well reviewed in Ref. 10 and 11, it too will only be briefly discussed. 

Amaut LG, Formosinho SJ (1998) Modelling intramolecular electron transfer reactions in cytochromes and in photosynthetic bacteria rection centres. J Photochem Photobiol A Chem... 

Although not related to iron and oxygen transport, it should be mentioned that synthetic biomimetic models of special pair bacteriochlorophyll a have also been prepared (247). The reason is that, in the molecular organization of chlorophyll in the photoreaction centers of both green plants and photosynthetic bacteria, it is believed that special pairs of chlorophyll molecules are oxidized in the primary light conversion event in photosynthesis. Dimeric chlorophyll derivatives such as the one in Fig. 6.6 in which the porphyrin... 

An Extended Model for Electron Spin Polarization in Photosynthetic Bacteria. ... 

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