Electron transport in mitochondria

An unusual [2Fe-2S] ferredoxin with unique spectroscopic properties exists in association with cytochromes b and c, and is involved in respiratory electron transport in mitochondria, chloroplasts and certain bacteria. When isolated, the complex contains two b hemes, one c, heme and the 2Fe-2S protein. The 2Fe-2S protein from the bct complex (Sections 62.1.5.2.3 and 62.1.5.2.5) was purified from bovine mitochondria by Rieske et al.,162 and is referred to as the Rieske iron-sulfur protein. The properties of this protein have been reviewed763 and its topography in mitochondrial ubiquinol-cytochrome c reductase has been described.764 They have high redox potentials in the range+150-330 mV. 

Figure 14-4 Schematic representation of electron transport in mitochondria.

Most of the components involved in electron transport in mitochondria are contained in four supramolecular protein complexes that traverse the inner mitochondrial membrane. Complex I, which contains FMN and various iron-sulfur clusters as active sites, transfers electrons from NADH to ubiquinone (Fig. 6-8). Complex II, which contains FAD, various iron-sulfur clusters, and a Cyt >, transfers electrons from succinate also to a ubiquinone. Ubiquinone functions as a pool of two-electron carriers, analogous to the function of plastoquinone A in the lamellar membranes of chloroplasts, which accepts electrons from Complexes I and II and delivers them to the... 

Vitamin E deficiency is also associated with impaired mitochondrial oxidative metabolism and impaired activity of microsomal cytochrome P450-dependent mixed-function oxidases, and hence the metabolism of xenobi-ofics. There is no evidence that vitamin E has any specific role in electron transport in mitochondria or microsomes. Again, changes in membrane lipids and oxidative damage presumably account for the observed metabolic abnormalities. 

Oxalate imposes an oxidant stress on renal cells by stimulating the generation of reactive oxygen species (ROS) [31]. ROS are produced as a byproduct of electron transport in mitochondria. Recent evidence suggests that mitochondria are a significant source of the ROS that are produced in renal cells following... 

Stigmatellin A is a powerful inhibitor of electron transport in mitochondria and chloroplasts. During the diastereo- and enantioselective total synthesis of this important natural product, D. Enders et al. utilized the Baker-Venkataraman rearrangement for the construction of the chromone system in good yield. ... 

Electron Transport in Mitochondria Is Coupled to Proton Translocation... 

FIG. 43 Electron-transport in mitochondria from body wall muscle of adult /4scaris suum. (1) NADH rhodoquinone reductase (complex I) (2) rhodoquinone (3) reduced rhodoquinone cytochrome C reductase (complex III) (4) reduced rhodoquinonerfumarate reductase (complex II) (5) electron-transfer fiavoprotein reductase (6) electron-transfer fiavoprotein (7) 2-methyl branched-chain enoyl CoA reductase. 

The use of respiratory inhibitors to determine the order of the electron transport chain depends on determining the relative amounts of oxidized and reduced forms of the various electron carriers in intact mitochondria. The logic of the experiment can be seen from the analogy of the blocked pipe. In this case, the reduced form of the carrier upstream (reduced carrier 2) accumulates because it cannot pass electrons farther in the chain. Likewise, the oxidized form of the carrier downstream (oxidized carrier 3) also accumulates because the supply of electrons that it could accept has been cut off (Figure 20.20). By use of careful techniques, intact mitochondria can be isolated from cells and can carry out electron transport if an oxidizable substrate is available. If electron transport in mitochondria occurs in the presence and absence of a respiratory inhibitor, different relative amounts of oxidized and reduced forms of the electron carriers will be present. 

Enzyme-catalyzed reactions Electron transport in mitochondria Signal transduction and gene expression Activation of nuclear transcription factors Oxidative damage to molecules, cells, and tissues Antimicrobial action of neutrophils and macrophages Aging and disease... 

I. Mechanism of toxicity. Phosphine Is a highly toxic gas, especially to the lungs, brain, kidneys, heart, and liver. The pathophysiologic action of phosphine is not clearly understood, but may be related to inhibition ot electron transport in mitochondria. Phosphides liberate phosphine gas upon contact with moisture, and this reaction is enhanced in the acidity of the stomach. Phosphine is then absorbed through the gastrointestinal and respiratory tracts. 

The rate of the electron transport in mitochondria was inhibited in both species grown in saline medium. 

With membrane-bound cytochrome c oxidase, an interesting route into mechanism and organization in intact redox systems is displayed. Hill and co-workers coupled [204] the electrochemistry of cytochrome c (as achieved at Au electrodes modifed by adsorption of bis(4-pyridyl)disulfide) to electron transport in mitochondria. A demonstration of the manner in which one may thus tap into the respiratory chain itself without using non-spedfic, small-molecule mediators is given in Fig. 24. Upon applying a potential of + 95 mV to an aerobic solution of cytochrome enclosed within a stirred reaction chamber, the electrolytic... 

Terpenoids represent a large class of natural products with numerous biological functions. Although terpenoids are usually regarded as secondary (plant) products, some of them are widespread and are involved in basic biological processes as electron transport in mitochondria and plastides. The name terpenoids is derived from turpentine, the aromatic resinlike exudations obtained from various coniferous trees. The common feature of all terpenoids is that they are built up by branched C5 units, isoprene (= 2-methylbutadiene). Terpenoids derived from just one isoprene unit are called hemiterpenes. 

Rieske protein is essential in the respiratory electron transport in mitochondria, chloroplasts and some bacteria. Its structure is quite different from other proteins containing [Fe2S2] in so far as the iron atom in Rieske protein is coordinated to two cysteines and two histidines. Miinck et al. investigated the EFG tensor of the ferrous site and found a fast relaxation between the two Zeeman levels of the S = 1/2 Kramers doublet leading to a diminished internal hyperfine field and a quasidiamagnetic spectrum in a filed of 4 T at 200 K, which is an indication of a magnetic splitting due to external field. ... 

Stigmatellin A [24] hi 2(X)0, the Enders group achieved the first total synthesis of stigmatellin A (58) [73], a natural product isolated by Hofle et al. [74] from myxobacterium Stigmatella aurantiaca, which is a powerful inhibitor of electron transport in mitochondria and chloroplasts. 

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