Bacterial photosynthetic membrane

In purple bacterial photosynthesis, light capture and energy transfer are efficiently accomplished by the strong cooperativity among different photosynthetic components, that is, LH complexes (LHl and LH2), reaction center (RC), c)Aochrome (c3A) bc  

In other Rhodobactor species, dimeric core complexes were seen in high-resolution AFM images. In native membranes of R. blasticus the core complexes possess (PufX2-LHli3-RCL,M,H 2 conformation, comprising two RCs surrounded by an S-shaped LHl assembly with two times 13 LHl a// heterodimers along with 2 PufX polypeptides 

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A kinetic model was developed to describe the pH-dependent uncoupling activity of substituted phenols in bacterial photosynthetic membranes [2]. In this model, the overall uncoupling activity is quantitatively separated into the contribution of membrane concentration, which can be estimated by the Kmw, and of intrinsic activity. The intrinsic activity of an uncoupler is influenced not only by the hydrophobicity and acidity, but also by steric effects and by the charge distribution within the molecule [2]. 

HJM Kramer, R van Grondelle, CN Hunter, WHJ Westerhuis and J Amesz (1984) Pigment organization of the B800-850 antenna complex of Rps. sphaeroides. Biochim Biophys Acta 765 156-165 TG Monger and WW Parson (1977) Singlet-triplet fusion in Rhodopsudomonas sphaeroides chromatophores. A probe of the organization of the photosynthetic apparatus. Biochim Biophys Acta 460 393-407 KR Miller (1979) Structure of a bacterial photosynthetic membrane. Proc Nat Acad Sci, USA 76 6415-6419. KR Miller (1982) Three-dimensional structure of a photosynthetic membrane. Nature 300 53-55... 

G Alegria and PL Dutton (1991) /. Langmuir-Biodgett monolayer films of bacterial photosynthetic membranes and isolated reaction centers preparation, spectrophotometric and electrochemical characterization. Biochim Biophys Acta 1057 239-257... 

Hara M, Majima T, Ajiki SI et al. Multilayer preparation of bacterial photosynthetic membrane with a certain orientation immobilized on the solid surface by avidin-biotin interaction. Bioelectrochem Bioenerg 1996 41 127-129. 

Miller KR. Structure of a bacterial photosynthetic membrane. Proc. Natl. Acad. Sci. USA 1979 76 6415-6419. 

Strongly curved membranes. For instance, in the study of bacterial photosynthetic membranes, a number of questions have not been addressed by AFM, like the location of the c d bc and ATPase complexes. The development of recognition imaging techniques, such as immuno-AFM, and the combination of AFM and confocal microscope are anticipated to overcome the difficulties. 

ASSOCIATIONS OF PIGMENT-PROTEIN COMPLEXES IN PHOSPHOLIPID ENRICHED BACTERIAL PHOTOSYNTHETIC MEMBRANES... 

Figure 12.12 X-ray diffraction pattern from crystals of a membrane-bound protein, the bacterial photosynthetic reaction center. (Courtesy of H. Michel.)...

Figure 12.22 Schematic diagram showing the flow of excitation energy in the bacterial photosynthetic apparatus. The energy of a photon absorbed by LH2 spreads rapidly through the periplasmic ring of bacterio-chlorophyll molecules (green). Where two complexes touch in the membrane, the energy can be transmitted to an adjacent LH2 ring. From there it passes by the same mechanism to LHl and is finally transmitted to the special chlorophyll pair in the reaction center. (Adapted from W. Kiihlbrandf, Structure 3 521-525, 1995.)...

Rees, D.C., et al. The bacterial photosynthetic reaction center as a model for membrane proteins. Anna. Rev. Biochem. 58 607-633, 1989. 

Fig. 5.2. The photosynthetic membrane of a green sulfur bacterium. The light-activated bacte-riochlorophyll molecule sends an electron through the electron-transport chain (as in respiration) creating a proton gradient and ATP synthesis. The electron eventually returns to the bacteri-ochlorophyll (cyclic photophosphorylation). If electrons are needed for C02 reduction (via reduction of NADP+), an external electron donor is required (sulfide that is oxidised to elemental sulfur). Note the use of Mg and Fe.

The photosynthetic reaction center (RC) of purple nonsulfur bacteria is the core molecular assembly, located in a membrane of the bacteria, that initiates a series of electron transfer reactions subsequent to energy transfer events. The bacterial photosynthetic RCs have been characterized in more detail, both structurally and functionally, than have other transmembrane protein complexes [1-52]. 

Q Yang, X-Y Liu, M Hara, P Lundahl, J Miyake. Quantitative affinity chromatographic studies of mitochondrial cytochrome c binding to bacterial photosynthetic reaction center, reconstituted in liposome membranes and immobilized by detergent dialysis and avidin-biotin binding. Anal Chem 280 94-102, 2000. 

Light-driven electron transfer in plant chloroplasts during photosynthesis is accomplished by multienzyme systems in the thylakoid membrane. Our current picture of photosynthetic mechanisms is a composite, drawn from studies of plant chloroplasts and a variety of bacteria and algae. Determination of the molecular structures of bacterial photosynthetic complexes (by x-ray crystallography) has given us a much improved understanding of the molecular events in photosynthesis in general. 

In green plants and algae, photosynthesis takes place in chloroplasts. The light reactions occur in the thylakoid membranes and the dark reactions take place in the stroma. In photosynthetic bacteria the light reactions take place in the bacterial plasma membrane, or in invaginations of it (chromatophores). 

Bacterial photosynthetic reaction centers (PRC) have been among the most actively studied ET proteins since DeVault and Chance first measured C. vinosum tunneling rates in the early 1960s. In many cases, measurements of ET kinetics preceded determination of the three-dimensional structure of the membrane-bound protein assembly. It was not until the X-ray crystal-stracture determinations of the Rhodopseudomonas (Rps.) viridus and Rhodobacter (Rb.) sphaeroides PRCs that distances could be assigned to specific rate constants. The recent crystal structures of photosystems l and from cyanobacteria promise to clarify critical aspects of the ET mechanisms in oxygenic PRC. ... 

The L and M subunits form the structural and functional core of the bacterial photosynthetic reaction center (see Figure 19.9). Each of these homologous subunits contains five transmembrane helices. The H subunit, which has only one transmembrane helix, lies on the cytoplasmic side of the membrane. The cytochrome subunit, which contains four c-type hemes, lies on the opposite periplasmic side. Four bacteriochlorophyll b (BChl-Z>) molecules, two bacteriopheophytin b (BPh) molecules, two quinones (Q and Qg), and a ferrous ion are associated with the L and M subunits. 

The most basic design requirements of the bacterial photosynthetic reaction centers then, are a light energy absorbing center and two chains of redox centers that connect this light-activatable center to cytochrome c and quinone on opposite sides of the membrane. The physical process by which electrons are transferred between members of the chains in reaction centers, and indeed in the vast majority of electron transfer proteins, was also revealed by Chance, together with Devault, in these same years [4]. 

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