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Photosynthetic bacteria, purple, cytochrome

Many cytochromes c are soluble but others are bound to membranes or to other proteins. A well-studied tetraheme protein binds to the reaction centers of many purple and green bacteria and transfers electrons to those photosynthetic centers.118 120 Cytochrome c2 plays a similar role in Rhodobacter, forming a complex of known three-dimensional structure.121 Additional cytochromes participate in both cyclic and noncyclic electron transport in photosynthetic bacteria and algae (see Chapter 23).120,122 124 Some bacterial membranes as well as those of mitochondria contain a cytochrome bct complex whose structure is shown in Fig. 18-8.125,126... [Pg.847]

In purple photosynthetic bacteria, electrons return to P870+ from the quinones QA and QB via a cyclic pathway. When QB is reduced with two electrons, it picks up protons from the cytosol and diffuses to the cytochrome bct complex. Here it transfers one electron to an iron-sulfur protein and the other to a 6-type cytochrome and releases protons to the extracellular medium. The electron-transfer steps catalyzed by the cytochrome 6c, complex probably include a Q cycle similar to that catalyzed by complex III of the mitochondrial respiratory chain (see fig. 14.11). The c-type cytochrome that is reduced by the iron-sulfur protein in the cytochrome be, complex diffuses to the reaction center, where it either reduces P870+ directly or provides an electron to a bound cytochrome that reacts with P870+. In the Q cycle, four protons probably are pumped out of the cell for every two electrons that return to P870. This proton translocation creates an electrochemical potential gradient across the membrane. Protons move back into the cell through an ATP-synthase, driving the formation of ATP. [Pg.340]

Figure 18 Schematic structure of the cytochrome bc complex from mitochondria. The struemre of the complex from purple photosynthetic bacteria is thought to be similar. The pathway of electron and proton transfer (modified Q-cycle) is overlaid on the schematic structure. Movement of the Rieske FeS protein is shown by the semitransparent yellow areas ... Figure 18 Schematic structure of the cytochrome bc complex from mitochondria. The struemre of the complex from purple photosynthetic bacteria is thought to be similar. The pathway of electron and proton transfer (modified Q-cycle) is overlaid on the schematic structure. Movement of the Rieske FeS protein is shown by the semitransparent yellow areas ...
In purple photosynthetic bacteria, and specifically in Rps. sphaeroides and Rps. capsulata, three cytochromes of b type have been identified by means of redox titration, in the dark, of isolated chromatophores [116]. They are characterized by midpoint potentials at pH = 7.0 equal to 0.155, 0.050 and -0.090 V (in Rps. sphaeroides)-, the of the 0.050 V species is pH dependent ( — 60 mV per pH unit) [116,117]. The presence of a cytochrome cc in these organisms, interfering spectrally with cytochrome b, makes the situation unclear as far as the existence of cyt. b E j = 0.155 V) is concerned [118]. The two other cytochromes E = 0.050 and — 0.090 V) have also been resolved kinetically in studies on the photosynthetic electron transport and on the basis of their spectral characteristics (band at 561 nm and a spht bands at 558 and 556 nm, respectively these two cytochromes will be referred to as 6-561 and 6-566 in the following) [119]. [Pg.119]

The location of cytochrome C2 in the periplasmic space of purple photosynthetic bacteria has been demonstrated directly by its prompt release following the preparation of sphaeroplasts, and by its accessibility to antibodies in these preparations [220]. Cytochromes c are oxidized in single turnover experiments with a biphasic kinetics (<1 2 and 200-400 /is) this pattern has been interpreted as due to the presence in chromatophores of both cyt. Cj and C2, which are oxidized in series [122]. [Pg.132]

Many cytochromes in energy-transducing organelles are membrane-bound proteins. Present in mitochondria and in purple photosynthetic bacteria, the cyt bc complex (also called ubiquinol-cytochrome c oxidoreductase, or complex III) catalyzes the electron transfer from ubiquinol to ferricyt c and pumps protons from the matrix to the cytosol.The catalytic core of the cyt bci complex comprises three redox-active subunits they are a cyt b with two ft-type hemes bn and bf), a cyt Cl, and a Reiske iron sulfur protein. While this catalytic core has enzymatic activity in some a proteobacteria like Paracoccus, Rhodospirillum rubrum, and Rb. capsulatus, mitochondrial cyt bci complexes have an additional seven or eight subunits." ... [Pg.47]

Phylogenetic tree of purple photosynthetic bacteria have recently been suggested based on the sequence analyses of 16S ribosomal RNA (4.) We have determined the types of RC in many non-sulfur purple bacteria and considered about their occurrence in the phylogenetic tree. It seems that the ancestral purple bacteria had the RC with the cytochrome subunit and the subunit has been lost mutationally at least in four independent lines. [Pg.193]

In contrast to common usage, the distinction between photosynthetic and respiratory Rieske proteins does not seem to make sense. The mitochondrial Rieske protein is closely related to that of photosynthetic purple bacteria, which represent the endosymbiotic ancestors of mitochondria (for a review, see also (99)). Moreover, during its evolution Rieske s protein appears to have existed prior to photosynthesis (100, 101), and the photosynthetic chain was probably built around a preexisting cytochrome be complex (99). The evolution of Rieske proteins from photosynthetic electron transport chains is therefore intricately intertwined with that of respiration, and a discussion of the photosynthetic representatives necessarily has to include excursions into nonphotosynthetic systems. [Pg.347]

Cytochromes b of mitochondrial membranes are involved in passing electrons from succinate to ubiquinone in complex II138 and also from reduced ubiquinone to cytochrome c, in the 248-kDa complex III (Fig. 18-8). A similar complex is present in photosynthetic purple bacteria.123 139 Cytochrome b560 functions in the transport of electrons from succinate dehydrogenase to ubiquinone,138 and cytochrome b561 of secretory vesicle membranes has a specific role in reducing ascorbic acid radicals.140... [Pg.848]

Bacterial photosynthesis. What is the relationship of the Z scheme of Fig. 23-17 to bacterial photosyntheses In photoheterotrophs, such as the purple Rhodospirillum, organic compounds, e.g., succinate, serve as electron donors in Eq. 23-30. Because they can utilize organic compounds for growth, these bacteria have a relatively low requirement for NADPH or other photochemically generated reductants and a larger need for ATP. Their photosynthetic reaction centers receive electrons via cytochrome c from succinate (E° ... [Pg.1301]

Many cytochromes c are soluble but others are bound to membranes or to other proteins. A well-studied tetraheme protein binds to the reaction centers of many purple and green bacteria and transfers electrons to those photosynthetic centers. Cytochrome... [Pg.847]

Fig. 7. A frame of reference for the Rp. viridis RC-associated cytochrome complex (A) and a more detailed view of the cytochrome subunit with the four hemes shown (B). See text for the various nomenclatures used. P represents the [BChllj (the primary donor). The table also includes the redox-potential values of the hemes, and the wavelength of the a-band of the hemes both at room and cryogenic temperatures. Figure (A) the same as Fig. 7 in Chapter 2. (B) is taken from CRD Lancaster, U Ermler and H Michel (1995) The structure of photosynthetic reaction centers from purple bacteria as revealed by X-ray crystallography. In RE Blankenship, MT Madigan and CE Bauer (eds) Anoxygenic Photosysnthetic Bacteria, p 511. Kluwer. Fig. 7. A frame of reference for the Rp. viridis RC-associated cytochrome complex (A) and a more detailed view of the cytochrome subunit with the four hemes shown (B). See text for the various nomenclatures used. P represents the [BChllj (the primary donor). The table also includes the redox-potential values of the hemes, and the wavelength of the a-band of the hemes both at room and cryogenic temperatures. Figure (A) the same as Fig. 7 in Chapter 2. (B) is taken from CRD Lancaster, U Ermler and H Michel (1995) The structure of photosynthetic reaction centers from purple bacteria as revealed by X-ray crystallography. In RE Blankenship, MT Madigan and CE Bauer (eds) Anoxygenic Photosysnthetic Bacteria, p 511. Kluwer.
Rhodospririllum rubrum is the most exhaustively studied of the purple nonsulfur bacteria. The photosynthetic apparatus is located in extensive infolded membrane vesicles called chromatophores. Cytochromes C2, cd, and 1)557.5 have all been found to be associated with the chromatophores (371), with C2 being the major component. Several lines of evidence, including fast kinetics following the excitation of the baeteriochlorophyll photocenter by laser flash, have suggested the scheme shown in Fig. 29, where cytochrome Cj is the immediate source of electrons to the electron-... [Pg.510]

It could be that the break between respiration and photosynthesis in these bacteria is more recent than we think. Cytochrome Ca has been suggested to have a respiratory as well as a photosynthetic role in R. spheroides (S72) and R. capsulata (372a-c) and no alternative respiratory chain has yet been identified in any of the Athiorhodaceae. In some of these organisms a situation may exist as in Fig. 46 with electrons flowing to both from light-excited bacteriochlorophyll and from external donors, and then from c either to an electron-depleted bacteriochlorophyll or to an oxidase molecule. This would account for the observed control mechanism in the purple nonsulfur bacteria. Under aerobic conditions in the dark, bacteriochlorophyll would not be electron-defi.cient, whereas the oxidase would be in its oxidized state and capable of accepting electrons from c. Under anaerobic conditions, electrons would reduce the oxidase, and further electron transfer down that path would be blocked. Light then would promote electrons away from bacteriochlorophyll and set cyclic photophosphorylation in motion. [Pg.541]

The literature on applications of advanced EPR methods for the characterization of paramagnetic sites in proteins is already quite large and growing fast. Instead of giving a review of all of these applications, the potential of these methods will be demonstrated on some of our own research examples. Examples will be shown on protein complexes of a) photosynthetic reaction centres of purple bacteria, b) soluble G-protein-nucleotide complexes with P2T and c) cytochrome c oxidase, a membrane-bound protein of the mitochondrial respiration chain. [Pg.120]

Two types of the photosynthetic reaction center (RC) complexes are known in pxirple bacteria, the distribution of which depends on bacterial species (1). In one type, the RC complexes have a cytochrome subunit with four c-type hemes. The other type of RC does not have the cytochrome subunit (Fig. 1). Three demensional structures of both types of RCs have been revealed in Rhodopseudomonas viridis (2) and Rhodobacter sphaeroides (3) the former has the bound cytochrome subunit. The major difference between the two types of RC is only in the presence or absence of the cytochrome subunit and the structure of the other three peptides with pigments and quinones is similar to each other. Evolutionary relationships between the two types of RC and the role of the bound cytochrome subunit are interesting subjects in the photosynthetic electron transfer system in purple bacteria. [Pg.193]

Erythrobacter sp. OCh 114 is a photosynthetic bacterium which adapts to aerobic environments (1-4). The amino acid sequence of its cytochrome 2 (cytochrome 55 ) indicated close relation of this species to the photosynthetic and non-photosynthetic species of the [Pg.2211]


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See also in sourсe #XX -- [ Pg.402 ]




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