Helminths: Comparison of their rhodoquinone

Allen, Patricia C.

doi:10.1016/0014-4894(73)90080-5

Cited by 31 publications

(18 citation statements)

References 19 publications

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“…In parasitic helminths, which also utilize fumarate as final electron acceptor during anoxia, Allen (11) demonstrated, however, the presence of RQ. Since RQ is present mainly in anaerobic, fumarate-reducing stages of parasitic helminths, it was suggested that rhodoquinol functions as electron donor in fumarate reduction, similar to menaquinol in fumarate reduction in other organisms (11). It is unknown whether RQ occurs only in parasitic helminths or is present in other fumarate-reducing eukaryotes as well, which would imply an important difference between prokaryotic and eukaryotic fumarate reduction (8 All examined mitochondria from eukaryotes contain Krebs cycle activity and a respiratory chain.…”

Section: Resultsmentioning

confidence: 99%

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Rhodoquinone and Complex II of the Electron Transport Chain in Anaerobically Functioning Eukaryotes

Hellemond

Klockiewicz

Gaasenbeek³

et al. 1995

Journal of Biological Chemistry

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Many anaerobically functioning eukaryotes have an anaerobic energy metabolism in which fumarate is reduced to succinate. This reduction of fumarate is the opposite reaction to succinate oxidation catalyzed by succinate-ubiquinone oxidoreductase, complex II of the aerobic respiratory chain. Prokaryotes are known to contain two distinct enzyme complexes and distinct quinones, menaquinone and ubiquinone (Q), for the reduction of fumarate and the oxidation of succinate, respectively. Parasitic helminths are also known to contain two different quinones, Q and rhodoquinone (RQ). This report demonstrates that RQ was present in all examined eukaryotes that reduce fumarate during anoxia, not only in parasitic helminths, but also in freshwater snails, mussels, lugworms, and oysters. It was shown that the measured RQ/Q ratio correlated with the importance of fumarate reduction in vivo. This is the first demonstration of the role of RQ in eukaryotes, other than parasitic helminths. Furthermore, throughout the development of the liver fluke Fasciola hepatica, a strong correlation was found between the quinone composition and the type of metabolism: the amount of Q was correlated with the use of the aerobic respiratory chain, and the amount of RQ with the use of fumarate reduction. It can be concluded that RQ is an essential component for fumarate reduction in eukaryotes, in contrast to prokaryotes, which use menaquinone in this process. Analyses of enzyme kinetics, as well as the known differences in primary structures of prokaryotic and eukaryotic complexes that reduce fumarate, support the idea that fumarate-reducing eukaryotes possess an enzyme complex for the reduction of fumarate, structurally related to the succinate dehydrogenasetype complex II, but with the functional characteristics of the prokaryotic fumarate reductases.Living with hypoxia or even anoxia is an everyday experience for many organisms. Not only many prokaryotes, but many eukaryotic organisms as well can function (temporarily) without oxygen. Parasitic helminths, freshwater snails, and some lower marine organisms are known to be able to survive anaerobic conditions by adaptation of their energy metabolism. In addition to simple fermentation in which glucose is degraded to ethanol or lactate, most of these facultative anaerobic eukaryotes contain another fermentation variant, malate dismutation (Fig. 1). Malate dismutation is found in both strictly and facultative anaerobically functioning prokaryotes as well as in some eukaryotes that are capable of functioning anaerobically, like parasitic helminths (1), freshwater snails (2), mussels (3), oysters (4), and lugworms and other marine invertebrates (5). Although several variations of malate dismutation with various end products occur, the use of the production of succinate as an electron sink is universal. The reduction of malate to succinate occurs in two reactions that reverse part of the Krebs cycle, and the reduction of fumarate is the essential NADHconsuming reaction to maintain redox balance. There...

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Section: Resultsmentioning

confidence: 99%

“…Free-living aerobic stages of several helminths contain a higher ratio of Q to RQ than parasitic anaerobic stages (11)(12)(13)(14). However, evidence for a quantitative correlation between the amount of RQ present and the importance of fumarate reduc-tion in the energy metabolism of parasitic helminths is still lacking.…”

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confidence: 99%

Rhodoquinone and Complex II of the Electron Transport Chain in Anaerobically Functioning Eukaryotes

Hellemond

Klockiewicz

Gaasenbeek³

et al. 1995

Journal of Biological Chemistry

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“…The use of the synthetic substrates ubiquinone-3 (UQ 3 ) and rhodoquinone-3 (RQ 3 ), where n ϭ 3 isoprene units (instead of 9 or 10 in the natural substrates), allow us to probe the Q-cycle and bypass reactions as well as to measure the relevant redox potentials of the electrochemical couples involved in these reactions. From these results we predict the potential impact due to bypass of the Q-cycle in organisms that contain a mixed UQ/RQ pool (32,37,48) and test the relationship between the rates of bypass reactions and the thermodynamic properties of these two substrates.…”

Section: The Cytochrome (Cyt)mentioning

confidence: 99%

The Respiratory Substrate Rhodoquinol Induces Q-cycle Bypass Reactions in the Yeast Cytochrome bc1 Complex

Cape¹,

Strahan

Lenaeus

et al. 2005

Journal of Biological Chemistry

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The mitochondrial cytochrome bc 1 complex catalyzes the transfer of electrons from ubiquinol to cyt c while generating a proton motive force for ATP synthesis via the "Q-cycle" mechanism. Under certain conditions electron flow through the Q-cycle is blocked at the level of a reactive intermediate in the quinol oxidase site of the enzyme, resulting in "bypass reactions," some of which lead to superoxide production. Using analogs of the respiratory substrates ubiquinol-3 and rhodoquinol-3, we show that the relative rates of Q-cycle bypass reactions in the Saccharomyces cerevisiae cyt bc 1 complex are highly dependent by a factor of up to 100-fold on the properties of the substrate quinol. Our results suggest that the rate of Q-cycle bypass reactions is dependent on the steady state concentration of reactive intermediates produced at the quinol oxidase site of the enzyme. We conclude that normal operation of the Q-cycle requires a fairly narrow window of redox potentials with respect to the quinol substrate to allow normal turnover of the complex while preventing potentially damaging bypass reactions. The cytochrome (cyt)2 bc 1 complex (EC 1.10.2.2) functions as the ubiquinol:cytochrome c oxidoreductase in the electron transport chains of mitochondria and bacteria, where it couples the energy released from the oxidation of ubiquinol (UQH 2 ) by high potential electron carriers (e.g. cyt c) to establish a proton motive force used to drive ATP synthesis (1, 2). Although the cyt bc 1 complex usually conserves energy across the membrane, deleterious side reactions can occur that bypass normal electron flow in the enzyme, robbing the cell of energy and potentially producing reactive oxygen species (3-7). To deal with this problem, the cyt bc 1 complex has apparently developed strict control mechanisms to prevent side reactions of ubiquinone/ubiquinol (UQ (1)/UQH 2 ; see The turnover mechanism of the cyt bc 1 complex is best described by the modified Q-cycle (11, 12). The key feature of this mechanism is the bifurcated oxidation of UQH 2 at the quinol oxidase (Q o ) site of the enzyme that sends one UQH 2 electron to a high potential chain (composed of the Rieske 2Fe2S cluster and cyt c 1 ), whereas the other electron reduces a low potential chain (cyt b L and b H ) and is eventually recycled back into the Q pool through UQ reduction at a quinone reductase (Q i ) site on the opposite side of the membrane. In most models UQH 2 oxidation proceeds by the initial reduction of the Rieske 2Fe2S cluster (13-15), which produces an unstable semiquinone (SQ) intermediate localized to the Q o site (SQ o ), which then reduces the low potential chain and UQ at the Q i site, leaving a labile UQ in the Q o pocket.Certain conditions such as mutation (16 -18), imposition of a high proton motive force (17,19,20), or inhibitor treatment (3-5, 7) cause interruption of electron flow from SQ o to the low potential chain and can lead to a large fraction of reactions that bypass the normal Q-cycle. Most Q-cycle bypass reactions are thought to ...

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“…The purple quinones were first discovered in the phototrophic bacterium Rhodospirillum rubrum (14), and later proved to occur as major quinone components together with ubiquinones in some other species of the purple nonsulfur bacteria (22) . Interestingly, rhodoquinones are also present in mitochondria of some eukaryotes, such as Astasia longa (3), Euglena gracilis (41), and anaerobic helminths (1,45). In the anaerobic eukaryotes, rhodoquinones function as mediators of anaerobic electron transport with fumarate as the terminal acceptor (12,51,52).…”

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confidence: 99%

Brachymonas denitrificans gen. nov., sp. nov., an aerobic chemoorganotrophic bacterium which contains rhodoquinones, and evolutionary relationships of rhodoquinone producers to bacterial species with various quinone classes.

Hiraishi

Sugiyama

Shin

1995

J. Gen. Appl. Microbiol.

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The new strains of aerobic chemoorganotrophic rhodoquinone-containing bacteria previously isolated from activated sludge were studied from taxonomic and phylogenetic viewpoints. These strains were Gramnegative, nonmotile coccobacilli, had a strictly respiratory type of metabolism with oxygen or nitrate as the terminal acceptor, produced catalase and oxidase, and contained both ubiquinone-8 and rhodoquinone-8 as major quinones. DNA-DNA reassociation studies revealed that the new strains were highly related to each other at hybridization levels of more than 74%, suggesting the genetic coherency of the isolates as a single species. The 16S rRNA gene from one of the isolates, strain AS-P1, was amplified in vitro and sequenced directly. Sequence comparisons and a distance matrix tree analysis revealed that strain AS-P 1 was most closely related to Comamonas testosteroni, a representative of the beta subclass of the Proteobacteria, but the level of sequence similarity between the two appeared to be low enough to warrant different generic allocations. The strains were differentiated from related organisms by a number of phenotypic and chemotaxonomic properties. Thus, we conclude that the isolates should be placed in a new genus and species of the beta subclass of the Proteobacteria, for which we propose the name Brachymonas denitrificans. Evolutionary relationships of rhodoquinone producers to bacterial species with various quinone classes were discussed on the basis of 16S rRNA sequence information.

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Helminths: Comparison of their rhodoquinone

Cited by 31 publications

References 19 publications

Rhodoquinone and Complex II of the Electron Transport Chain in Anaerobically Functioning Eukaryotes

Rhodoquinone and Complex II of the Electron Transport Chain in Anaerobically Functioning Eukaryotes

The Respiratory Substrate Rhodoquinol Induces Q-cycle Bypass Reactions in the Yeast Cytochrome bc1 Complex

Brachymonas denitrificans gen. nov., sp. nov., an aerobic chemoorganotrophic bacterium which contains rhodoquinones, and evolutionary relationships of rhodoquinone producers to bacterial species with various quinone classes.

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