Cytochrome bcj complex

Hunte, C., Koepke, J., Lange, C., Rossmanith, T. and Michel, H. (2000) Structure at 2.3 A resolution of the cytochrome bcj complex from the yeast Saccharomyces cerevisiae with an antibody Fv fragment, Structure, 8, 669-684. 

It has long been assumed that azurin is an in vivo electron donor to cytochrome cdj of P. aeruginosa. However, construction of mutants of P. aeruginosa in which one or both of the genes for azurin and cytochrome C551 have been deleted has led to the conclusion that in vivo cytochrome C is essential, but that azurin is ineffective, for the donation of electrons to the nitrite reductase (Vijgenboom et al.. 1997). The discrepaney between in vivo and in vitro observations eould be reconciled if it is the failure of azurin to except electrons from the cytochrome bcj complex, or other donor, that is responsible for its ineffectiveness in vivo. 

Crofts, A. R., and Berry, E. A., 1998, Structure and function of cytochrome bcj complex of mitochondria and photosynthetic bacteria, Curr. Opin. in Struct. Biol. 8 501n509. 

The reaction centre can also be viewed as an enzyme, namely a cytochrome C2 ubiquinone oxidoreductase (Figure 3B). This enzyme uses light to power an energetically-unfavourable reaction, the reduction of UQjq by reduced cytochrome C2 (cytc ). The products of reaction centre enzymatic activity, oxidised cytochrome C2 (cyt c ). and reduced ubiquinone (UQjjH2) are the substrates for cytochrome bCj complex, which catalyses the reduction of cyt by UQ1QH2. 

Complex III transfers electrons from reduced coenzyme Q (UQH2) to cytochrome c. Because it contains two b-type cytochromes, one cytochrome Cj (cyt Cj), and one iron-sulfur center, complex III is sometimes referred to as the cytochrome bcj complex. The cytochromes (Figure 10.6) are a series of electron transport proteins that contain a heme prosthetic group similar to those found in hemoglobin and myoglobin. Electrons are transferred one at a time as each oxidized iron atom (Fe3+) is reversibly reduced to Fe2+. The movement of electrons from UQH2 to cytochrome c is a complex, multistep process. Because UQ is lipid-soluble, it diffuses within the inner membrane between the electron donors in complex I or II and the electron acceptor in complex... 

I-III as pictured in Fig. 18-5. One site of pumping is known to be in the cytochrome c oxidase complex. When reconstituted into phospholipid, the purified complex does pump protons in response to electron transport, H+/e ratios of 1 being observed. 437,i47,i9i As mentioned in Section B,3 a large amoimt of experimental effort has been devoted to identifying proton transport pathways in cytochrome c oxidase and also in the cytochrome bcj (complex II). Proton pumping appears to be coupled to chemical changes occurring between intermediates P and F of Fig. 18-11, between F and and possibly between O and r3 7138... 

Figure 23-32 Simplified diagram of cyclic electron flow in purple bacteria. Two protons from the cytoplasm bind to in the reaction center to form QH2 (ubiquinol), which diffuses into the ubiquinone pool. From there it is dehydrogenated by the cytochrome bcj complex with expulsion of two protons into the periplasm. A third and possibly a fourth proton may be pumped (green arrows) across the membrane, e.g., via the Q cycle (Fig. 18-9). The protons are returned to the cytoplasm through ATP synthase with formation of ATP. Some electrons may flow to the reaction centers from such reduced substrates as S and some electrons may be removed to generate NADPH using reverse electron transport. ...

Complex m (uhiquinol-cytochrome c oxido-reductase or cytochrome bcj complex). Mitochondrial complex 111 is a dimeric complex, each subunit of which contains 11 different subunits with a total molecular mass of 240 kDa per monomer. ° ° However, in many bacteria the complex consists of only three subunits, cytochrome b, cytochrome Cj, and the high potential ( 0.3 V) Rieske iron-sulfur protein, which is discussed in Chapter 16, Section A,7. These three proteins are present in all bc complexes. 

S Iwata, M Saynovits, TA Link, H Michel. Structure of the water soluble fragment of the Rieske iron-sulfur protein of the bovine heart mitochondrial cytochrome bcj complex determined by MAD phasing at 1.5 A resolution. Structure 4 567-579, 1996. 

HQNO (1) and A -deoxy-HQNO (2) have weak activity against Gram-positive bacteria, 1 inhibits the mitochondrial respiratory chain in the cytochrome bCj complex, 5-lipoxygenase, and is an antagonist to the antibacterial activity of dihydrostreptomycin. 

Complex III The cytochrome bcj complex oxidizes 2 molecules of ubiquinol, pumps 4 protons into the intermembrane (cytosolic) space, and reduces two molecules of cytochrome c. Overall equation ... 

C Lange and C. Hunte, Crystal Structure of the Yeast Cytochrome bcj Complex with its Bound Substrate Cytochrome c. Proc. NatL Acad. Sci. U.SA., 99,2800-2 )5,2002. 

In the mitochondrial electron transport chain, electrons move from an electron donor (NADH, FADH, or QHj) to a terminal electron acceptor (O2) via a series of redox reactions. Complex III is called the cytochrome bcj complex. Complex IV is the end station where oxygen molecules are accepting electrons and protons and are reduced to water. Complex IV is also called cytochrome c oxidase (CcO). 

Keywords Gluconobacter oxydans 621H Cyclic pentose phosphate pathway Cytochrome bd Cytochrome bos Cytochrome bcj complex Genome-wide transcriptome analysis C-Metabolic flux analysis... 

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