Respiration electron transport system

Inhibition of cytochromes of electron transport system can be caused by cyanogenic glycosides, such as amygdalin (Fig. 11.14) in bitter almonds, Prunus amygdalus, linamarin and lotaustralin in clover and birdsfoot trefoil, or dhurrin (Fig. 11.14) in Sorghum vulgare. The potent effect of cyanide on cell respiration has given rise to a recent serious conservation problem. In Southeast Asia, divers stun fish on coral reefs with a blast of cyanide to collect them for the aquarium trade. In the process, many fish are killed and the corals bleached, because their symbionts die (e.g. Payne, 2001). 

Aerobic respiration can be subdivided into a number of distinct but coupled processes, such as the carbon flow pathways resulting in the production of carbon dioxide and the oxidation of NADH + H+ and FADH2 (flavin adenine dinucleotide) to water via the electron transport systems or the respiratory chain. 

The reason for the presence of the alternate pathway is not clear. One possible function is that when significantly increased levels of intermediates are needed during periods of high metabolic activity, their rate of synthesis is limited by the rate of the electron transport system. The alternate pathway may provide an unrestricted means of accelerating respiration and the production of the required intermediates. The alternative pathway s relationship to certain developmental processes supports this possibility. For example, cyanide inhibits the respiration of dormant tubers more than... 

Four electron carriers (A, B, C, and D) are required in the electron transport system of a recently discovered aerobic bacterium. You find that in the presence of substrate and 02, four inhibitors (I, II, III, and IV) block respiration at four different sites. From differential spectrophotometry of the electron carriers, you find that these inhibitors yield the patterns of oxidation state of the carriers shown below. What... 

Naqvi, S. W. A., and Shailaja, M. S. (1993). Activity of the respiratory electron transport system and respiration rates within the oxygen minimum layer of the Arabian Sea. Deep Sea Res. I. 40, 687-696. 

Oxidative phosphorylation is the process in which ATP molecules are formed as a result of the transfer of electrons from the reducing equivalents, NADH or FADH2 (produced by glycolysis, the citric acid cycle and fatty acid oxidation) to oxygen by a series of electron carriers in the form of a chain located in the inner membrane of mitochondria. This is the final reaction sequence of respiration. Since the electrons are transferred by a series of electron carriers in the form of a chain, it is known as electron transport system (ETS). 

Based on the structural similarity between the piercidines and co-enzyme Q, several research groups presumed and supported experimentally that the effect of the piercidines is based on competitive inhibition of the mitochondrial electron-transport systems (Hall et al., 1966 Jeng et al., 1968 Morgan et al., 1968 Morgan and Singer, 1967 Mitsui et al., 1969). Both piercidine A and piercidine B inhibit respiration at very low concentrations (Tamura et al., 1963). 

The toxicity of cyanide is attributed to its ability to inhibit enzyme reactions. The action of one such enzyme, cytochrome oxidase, essential for the respiration of cells is inhibited by cyanide ions. Cytochrome oxidase is a component of the mitochondrial electron transport system. It transfers electrons from cytochrome c to oxygen, forming water, while releasing sufficient free energy to permit the formation of adenosine 5 -triphosphate (ATP). The latter is essential for normal metabolic processes. Cyanide ion forms complexes with heavy metal ions such as iron and copper to stop electron transport and thus prevent ATP formation. Several enzyme reactions have been listed that cyanide can inhibit several enzyme reactions by forming complexes. 

One mechanism that has been proposed to explain the hepatotoxicity of 1,1,2-trichloroethane is the generation of free radical intermediates from reactive metabolites of 1,1,2-trichloroethane (acyl chlorides). Free radicals may stimulate lipid peroxidation which, in turn, may induce liver injury (Albano et al. 1985). However, Klaassen and Plaa (1969) found no evidence of lipid peroxidation in rats given near-lethal doses of 1,1,2-trichloroethane by intraperitoneal injection. Takano and Miyazaki (1982) determined that 1,1,2-trichloroethane inhibits intracellular respiration by blocking the electron transport system from reduced nicotinamide adenine dinucleotide (NADH) to coenzyme Q (CoQ), which would deprive the cell of energy required to phosphorylate adenosine diphosphate (ADP) and thereby lead to depletion of energy stores. 

Energy conservation via polysulfide sulfur respiration in Bacteria and Archaea appears to be similar. Membrane bound respiratory chains generate a chemios-motic potential, which is utilized by membrane bound ATP synthases to form ATP. Yet, due to their extreme habitats, thermophiles like A. ambivalens and hyperthermophiles like P. abyss may have adapted their electron transport systems to high temperatures by forming stable electron transport complexes in contrast to the mesophilic bacteria W. succinogenes. 

Another promising biochemical approach, which may be linked to the deterioration of the hemopoitic system, involves the subcellular effects of lead on mitochondria. In experiments described by Brierley (2), lead at the micromolar level was shown to have a variety of effects centering around the inhibition of respiration and breakdown of the regulation of mitochondrial membrane permeability. The uptake of lead into the mitochondrial matrix is closely related to the membrane transport mechanism(s) for calcium. Since lead is known to inhibit several enzymes of the Kreb s cycle and the electron transport system, heme synthesis may be inhibited at the mitochon-... 

Electron transport systems perform important functions concerning respiration and energy metabolism in eucaryotes [22, 23], The electron transport reactions occur at the mitochondria inner membrane formed by electron transport proteins [24] and the lipid bilayer built up by the self-assembly of phospholipids as vital smfactants [25, 26]. The electron transport proteins include redox catalysts such as nicotinamide, iron [27, 28], and quinones [29]. The electrons produced by these redox reactions transfer through the lipid bilayer. While the relationship between the electron transport mechanisms and the molecular self-assembly in vivo has been clarified, control of the self-assembly by electron transport has been applied for an artificial polymeric surfactant. 

Mitochondria are associated with (/) the components of the electron transport system (respiratory chain), (//) the synthesis of ATP during respiration, and iiii) the oxidative reactions of the tricarboxylic acid (Krebs ) cycle. 

Low concentrations of antimycin A were found in 1949 to inhibit almost completely the oxygen uptake of respiring yeasti29. Later it was shown that the antibiotic is a powerful inhibitor of succinoxidase. Chance and Willi-ams o have established that antimycin A inactivates a specific component of the electron transport system in mitochondria, with the result that reduced cytochrome b is not oxidised by cytochrome c. The antibiotic... 

Antimycin A and usnic acid inhibit respiration at a site in the terminal electron transport system between cytochromes b and The binding... 

In aerobiosis, the electrons and protons are transported to oxygen, which is most often reduced to water. This process is called aerobic respiration. The transport system consists of a group of cytochromes. The proton flux creates a proton motive force, which permits the synthesis of ATP molecules. The conservation of the oxidation energy is ensured by the synthesis of the pyrophosphate bond of ATP. This bond generates energy when it is hydrolyzed. This system does not exist in lactic acid bacteria, although some species can synthesize cytochromes from precursors. 

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