ubiquinone and rhodoquinone

The terpenoid benzoquinone, rhodoquinone (RQ), is essential to the bioenergetics of many organisms that survive in low oxygen environments. RQ biosynthesis and its regulation has potential as a novel target for anti-microbial and anti-parasitic drug development. Recent work has uncovered two distinct pathways for RQ biosynthesis which have evolved independently. The first pathway is used by bacteria, such as Rhodospirillum rubrum, and some protists that possess the rquA gene. These species derive their RQ directly from ubiquinone (UQ), the essential electron transporter used in the aerobic respiratory chain. The second pathway is used in animals, such as Caenorhabditis elegans and parasitic helminths, and requires 3-hydroxyanthranilic acid (3-HAA) as a precursor, which is derived from tryptophan through the kynurenine pathway. A COQ-2 isoform, which is unique to these species, facilitates prenylation of the 3-HAA precursor. After prenylation, the arylamine ring is further modified to form RQ using several enzymes common to the UQ biosynthetic pathway. In addition to current knowledge of RQ biosynthesis, we review the phylogenetic distribution of RQ and its function in anaerobic electron transport chains in bacteria and animals. Finally, we discuss key steps in RQ biosynthesis that offer potential as drug targets to treat microbial and parasitic infections, which are rising global health concerns.

Topics: Anaerobiosis; Animals; Bacteria; Biosynthetic Pathways; Electron Transport; Electrons; Energy Metabolism; Ubiquinone

Mitochondria are usually considered to be the powerhouses of the cell and to be responsible for the aerobic production of ATP. However, many eukaryotic organisms are known to possess anaerobically functioning mitochondria, which differ significantly from classical aerobically functioning mitochondria. Recently, functional and phylogenetic studies on some enzymes involved clearly indicated an unexpected evolutionary relationship between these anaerobically functioning mitochondria and the classical aerobic type. Mitochondria evolved by an endosymbiotic event between an anaerobically functioning archaebacterial host and an aerobic alpha-proteobacterium. However, true anaerobically functioning mitochondria, such as found in parasitic helminths and some lower marine organisms, most likely did not originate directly from the pluripotent ancestral mitochondrion, but arose later in evolution from the aerobic type of mitochondria after these were already adapted to an aerobic way of life by losing their anaerobic capacities. This review will focus on some biochemical and evolutionary aspects of these fermentative mitochondria, with special attention to fumarate reductase, the synthesis of the rhodoquinone involved, and the enzymes involved in acetate production (acetate : succinate CoA-transferase and succinyl CoA-synthetase).

Topics: Acetates; Aerobiosis; Anaerobiosis; Animals; Biological Evolution; Electron Transport; Fermentation; Mitochondria; Phylogeny; Succinate Dehydrogenase; Ubiquinone

Parasites have developed a variety of physiological functions necessary for their survival within the specialized environment of the host. Using metabolic systems that are very different from those of the host, they can adapt to low oxygen tension present within the host animals. Most parasites do not use the oxygen available within the host to generate ATP, but rather employ anaerobic metabolic pathways. In addition, all parasites have a life cycle. In many cases, the parasite employs aerobic metabolism during its free-living stage outside the host. In such systems, parasite mitochondria play diverse roles. In particular, marked changes in the morphology and components of the mitochondria during the life cycle are very interesting elements of biological processes such as developmental control and environmental adaptation. Recent research on the respiratory chain of the parasitic helminth Ascaris suum has shown that the mitochondrial NADH-fumarate reductase system plays an important role in the anaerobic energy metabolism of adult parasites inhabiting hosts, as well as describing unique features of the developmental changes that occur during its life cycle.

Topics: Anaerobiosis; Animals; Ascaris suum; DNA, Mitochondrial; Electron Transport; Evolution, Molecular; Fatty Acid Desaturases; Life Cycle Stages; Mitochondria; Models, Biological; Models, Molecular; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Phosphoenolpyruvate Carboxykinase (ATP); Succinic Acid; Ubiquinone

Many lower eukaryotes can survive anaerobic conditions via a fermentation pathway that involves the use of the reduction of endogenously produced fumarate as electron sink. This fumarate reduction is linked to electron transport in an especially adapted, anaerobically functioning electron-transport chain. An aerobic energy metabolism with Krebs cycle activity is accompanied by electron transfer from succinate to ubiquinone via complex II of the respiratory chain. On the other hand, in an anaerobic metabolism, where fumarate functions as terminal electron acceptor, electrons are transferred from rhodoquinone to fumarate, which is the reversed direction. Ubiquinone cannot replace rhodoquinone in the process of fumarate reduction in vivo, as ubiquinone can only accept electrons from complex II and cannot donate them to fumarate. Rhodoquinone, with its lower redox potential than ubiquinone, is capable of donating electrons to fumarate. Eukaryotic fumarate reductases were shown to interact with rhodoquinone (a benzoquinone), whereas most prokaryotic fumarate reductases interact with the naphtoquinones menaquinone and demethylmenaquinone. Fumarate reductase, the enzyme essential for the anaerobic functioning of many eukaryotes, is structurally very similar to succinate dehydrogenase, the Krebs cycle enzyme catalysing the reverse reaction. In prokaryotes these enzymes are differentially expressed depending on the external conditions. Evidence is now emerging that also in eukaryotes two different enzymes exist for succinate oxidation and fumarate reduction that are differentially expressed.

Topics: Anaerobiosis; Animals; Electron Transport; Electron Transport Complex II; Energy Metabolism; Eukaryotic Cells; Multienzyme Complexes; NAD(P)H Dehydrogenase (Quinone); Oxidoreductases; Succinate Dehydrogenase; Ubiquinone; Vitamin K

Soil transmitted helminths (STHs) are major human pathogens that infect over a billion people. Resistance to current anthelmintics is rising and new drugs are needed. Here we combine multiple approaches to find druggable targets in the anaerobic metabolic pathways STHs need to survive in their mammalian host. These require rhodoquinone (RQ), an electron carrier used by STHs and not their hosts. We identified 25 genes predicted to act in RQ-dependent metabolism including sensing hypoxia and RQ synthesis and found 9 are required. Since all 9 have mammalian orthologues, we used comparative genomics and structural modeling to identify those with active sites that differ between host and parasite. Together, we found 4 genes that are required for RQ-dependent metabolism and have different active sites. Finding these high confidence targets can open up in silico screens to identify species selective inhibitors of these enzymes as new anthelmintics.

Topics: Animals; Anthelmintics; Catalytic Domain; Computer Simulation; Helminth Proteins; Helminthiasis; Helminths; Humans; Ubiquinone

Parasitic helminths use two benzoquinones as electron carriers in the electron transport chain. In normoxia, they use ubiquinone (UQ), but in anaerobic conditions inside the host, they require rhodoquinone (RQ) and greatly increase RQ levels. We previously showed the switch from UQ to RQ synthesis is driven by a change of substrates by the polyprenyltransferase COQ-2 (Del Borrello et al., 2019; Roberts Buceta et al., 2019); however, the mechanism of substrate selection is not known. Here, we show helminths synthesize two

Topics: Alkyl and Aryl Transferases; Alternative Splicing; Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Nematoda; Oxidation-Reduction; Platyhelminths; Ubiquinone

The lipophilic electron-transport cofactor rhodoquinone (RQ) facilitates anaerobic metabolism in a variety of bacteria and selected eukaryotic organisms in hypoxic environments. We have shown that an intact rquA gene in Rhodospirillum rubrum is required for RQ production and efficient growth of the bacterium under anoxic conditions. While the explicit details of RQ biosynthesis have yet to be fully delineated, ubiquinone (Q) is a required precursor to RQ in R. rubrum, and the RquA gene product is homologous to a class I methyltransferase. In order to identify any additional requirements for RQ biosynthesis or factors influencing RQ production in R. rubrum, we performed transcriptome analysis to identify differentially expressed genes in anoxic, illuminated R. rubrum cultures, compared with those aerobically grown in the dark. To further select target genes, we employed a bioinformatics approach to assess the likelihood that a given differentially expressed gene under anoxic conditions may also have a direct role in RQ production or regulation of its levels in vivo. Having thus compiled a list of candidate genes, nine were chosen for further study by generation of knockout strains. RQ and Q levels were quantified using liquid chromatography-mass spectrometry, and rquA gene expression was measured using the real-time quantitative polymerase chain reaction. In one case, Q and RQ levels were decreased relative to wild type; in another case, the opposite effect was observed. These results comport with the crucial roles of rquA and Q in RQ biosynthesis, and reveal the existence of potential modulators of RQ levels in R. rubrum.

Topics: Base Sequence; Biosynthetic Pathways; Chromatography, Liquid; DNA, Bacterial; Gene Expression; Gene Knockout Techniques; Genes, Bacterial; Rhodospirillum rubrum; Spectrometry, Mass, Electrospray Ionization; Ubiquinone

Terpenoid quinones are liposoluble redox-active compounds that serve as essential electron carriers and antioxidants. One such quinone, rhodoquinone (RQ), couples the respiratory electron transfer chain to the reduction of fumarate to facilitate anaerobic respiration. This mechanism allows RQ-synthesizing organisms to operate their respiratory chain using fumarate as a final electron acceptor. RQ biosynthesis is restricted to a handful of prokaryotic and eukaryotic organisms, and details of this biosynthetic pathway remain enigmatic. One gene, rquA, was discovered to be required for RQ biosynthesis in Rhodospirillum rubrum. However, the function of the gene product, RquA, has remained unclear. Here, using reverse genetics approaches, we demonstrate that RquA converts ubiquinone to RQ directly. We also demonstrate the first in vivo synthetic production of RQ in Escherichia coli and Saccharomyces cerevisiae, two organisms that do not natively produce RQ. These findings help clarify the complete RQ biosynthetic pathway in species which contain RquA homologs.

Topics: Bacterial Proteins; Biosynthetic Pathways; Escherichia coli; Oxidation-Reduction; Recombinant Proteins; Rhodospirillum rubrum; Saccharomyces cerevisiae; Substrate Specificity; Ubiquinone

A key metabolic adaptation of some species that face hypoxia as part of their life cycle involves an alternative electron transport chain in which rhodoquinone (RQ) is required for fumarate reduction and ATP production. RQ biosynthesis in bacteria and protists requires ubiquinone (Q) as a precursor. In contrast, Q is not a precursor for RQ biosynthesis in animals such as parasitic helminths, and most details of this pathway have remained elusive. Here, we used

Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Chromatography, High Pressure Liquid; Hydrolases; Kynurenine; Kynurenine 3-Monooxygenase; Mass Spectrometry; Methyltransferases; Mitochondria; RNA Interference; RNA, Double-Stranded; Subcutaneous Tissue; Ubiquinone

Parasitic helminths infect over a billion humans. To survive in the low oxygen environment of their hosts, these parasites use unusual anaerobic metabolism - this requires rhodoquinone (RQ), an electron carrier that is made by very few animal species. Crucially RQ is not made or used by any parasitic hosts and RQ synthesis is thus an ideal target for anthelmintics. However, little is known about how RQ is made and no drugs are known to block RQ synthesis.

Topics: Anaerobiosis; Animals; Caenorhabditis elegans; Hypoxia; Kynurenine; Metabolic Networks and Pathways; Survival Analysis; Ubiquinone

Under hypoxic conditions, some organisms use an electron transport chain consisting of only complex I and II (CII) to generate the proton gradient essential for ATP production. In these cases, CII functions as a fumarate reductase that accepts electrons from a low electron potential quinol, rhodoquinol (RQ). To clarify the origins of RQ-mediated fumarate reduction in eukaryotes, we investigated the origin and function of

Topics: Adaptation, Biological; Anaerobiosis; Bacteria; Electron Transport Complex II; Eukaryota; Fumarates; Gene Transfer, Horizontal; Genetic Variation; Oxidation-Reduction; Phylogeny; Ubiquinone

The second electron transfer from primary ubiquinone Q(A) to secondary ubiquinone Q(B) in the reaction center (RC) from Rhodobacter sphaeroides involves a protonated Q(B)(-) intermediate state whose low pK(a) makes direct observation impossible. Here, we replaced the native ubiquinone with low-potential rhodoquinone at the Q(B) binding site of the M265IT mutant RC. Because the in situ midpoint redox potential of Q(A) of this mutant was lowered approximately the same extent (≈100 mV) as that of Q(B) upon exchange of ubiquinone with low-potential rhodoquinone, the inter-quinone (Q(A) → Q(B)) electron transfer became energetically favorable. After subsequent saturating flash excitations, a period of two damped oscillations of the protonated rhodosemiquinone was observed. The Q(B)H(•) was identified by (1) the characteristic band at 420 nm of the absorption spectrum after the second flash and (2) weaker damping of the oscillation at 420 nm (due to the neutral form) than at 460 nm (attributed to the anionic form). The appearance of the neutral semiquinone was restricted to the acidic pH range, indicating a functional pK(a) of <5.5, slightly higher than that of the native ubisemiquinone (pK(a) < 4.5) at pH 7. The analysis of the pH and temperature dependencies of the rates of the second electron transfer supports the concept of the pH-dependent pK(a) of the semiquinone at the Q(B) binding site. The local electrostatic potential is severely modified by the strongly interacting neighboring acidic cluster, and the pK(a) of the semiquinone is in the middle of the pH range of the complex titration. The kinetic and thermodynamic data are discussed according to the proton-activated electron transfer mechanism combined with the pH-dependent functional pK(a) of the semiquinone at the Q(B) site of the RC.

Topics: Amino Acid Substitution; Bacterial Proteins; Binding Sites; Electron Transport; Kinetics; Mutation; Photosynthetic Reaction Center Complex Proteins; Protons; Rhodobacter sphaeroides; Static Electricity; Thermodynamics; Ubiquinone

A Gram-stain-negative, rod-shaped, phototrophic bacterium, strain JA793(T), was isolated from rhizosphere soil of paddy. The strain was capable of growing phototrophically and chemotrophically. Bacteriochlorophyll-a and carotenoids of the spirilloxanthin series were present as photosynthetic pigments. The major fatty acid of strain JA793(T) was C18 : 1ω7c/C18 : 1ω6c (>65.7%), with minor amounts of C16 : 0, C16 : 1ω7c/C16 : 1ω6c, C20 : 2ω6,9c, C16 : 0 3-OH, C14 : 0 and C18 : 0 also present. Ubiquinone-10 and rhodoquinone-10 were present as primary quinones. Phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine were the major polar lipids, while minor amounts of amino lipids and unidentified lipids were also present. The G+C content of genomic DNA of strain JA793(T) was 68.7 mol%. 16S rRNA gene-based EzTaxon-e blast search analysis of strain JA793(T) indicated highest sequence similarity with members of the genus Rhodoplanes in the family Hyphomicrobiaceae of the class Alphaproteobacteria. Strain JA793(T) had high sequence similarity with Rhodoplanes elegans AS130(T) (98.6%), Rhodoplanes roseus 941(T) (98%), Rhodoplanes pokkaliisoli JA415(T) (97.5%) and Rhodoplanes piscinae JA266(T) (97.3%) and other members of the genus Rhodoplanes (<97%). However, strain JA266(T) was related by <59% (based on DNA-DNA hybridization) to Rhodoplanes elegans DSM 11907(T) ( = AS130(T)), Rhodoplanes roseus DSM 5909(T) ( = 941(T)), Rhodoplanes pokkaliisoli JA415(T) and Rhodoplanes piscinae JA266(T). The genomic information was well supported by phenotypic and chemotaxonomic data to classify strain JA793(T) as a representative of a novel species in the genus Rhodoplanes, for which the name Rhodoplanes oryzae sp. nov. is proposed. The type strain is JA793(T) ( = NBRC 109406(T) = KCTC 15260(T)).

Topics: Bacterial Typing Techniques; Base Composition; DNA, Bacterial; Fatty Acids; Hyphomicrobiaceae; India; Molecular Sequence Data; Nucleic Acid Hybridization; Oryza; Phylogeny; Rhizosphere; RNA, Ribosomal, 16S; Sequence Analysis, DNA; Soil Microbiology; Ubiquinone

A reddish-brown bacterium, designated strain JA318(T), was purified from a photoheterotrophic enrichment culture obtained from the rhizosphere soil of paddy. Cells of strain JA318(T) are spiral shaped, Gram-stain-negative and motile by means of amphitrichous flagella. Strain JA318(T) has no NaCl requirement for growth but can tolerate up to 1.5 % (w/v) NaCl. Internal photosynthetic membranes are present as lamellar stacks. Photoorganoheterotrophy is the only growth mode observed. Strain JA318(T) contains bacteriochlorophyll a, lycopene and rhodopin as major carotenoids. Thiamine, niacin and para-aminobenzoic acid (PABA) are required as growth factors. Major fatty acids are C18 : 1ω7c and C16 : 0. Ubiquinone-8 and rhodoquinone-8 are the observed quinones. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified aminolipid are the major polar lipids in strain JA318(T). Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain JA318(T) clustered with species of the genus Rhodospirillum which belongs to the class Alphaproteobacteria. The highest sequence similarity of strain JA318(T) was found with Rhodospirillum sulfurexigens JA143(T) (99.9 %). The DNA-DNA reassociation values of strain JA318(T) with Rsp. sulfurexigens JA143(T) and Rhodospirillum photometricum DSM 122(T) were 52 ± 2 % and 45 ± 1 %, respectively. The genomic DNA G+C content of strain JA318(T) was 60.2 mol%. Based on the morphological, physiological, chemotaxonomical and molecular evidence, strain JA318(T) is significantly different from the type strains of species of the genus Rhodospirillum, of the family Rhodospirillaceae, and it is proposed that the strain be classified as a representative of a novel species for which the name Rhodospirillum oryzae sp. nov. is proposed. The type strain is JA318(T) (= KCTC 5960(T) = NBRC 107573(T)).

Topics: Bacterial Typing Techniques; Bacteriochlorophyll A; Base Composition; Carotenoids; DNA, Bacterial; Fatty Acids; India; Lycopene; Molecular Sequence Data; Nucleic Acid Hybridization; Oryza; Phylogeny; Rhizosphere; Rhodospirillum; RNA, Ribosomal, 16S; Sequence Analysis, DNA; Soil Microbiology; Ubiquinone

Rhodoquinone (RQ) is a required cofactor for anaerobic respiration in Rhodospirillum rubrum, and it is also found in several helminth parasites that utilize a fumarate reductase pathway. RQ is an aminoquinone that is structurally similar to ubiquinone (Q), a polyprenylated benzoquinone used in the aerobic respiratory chain. RQ is not found in humans or other mammals, and therefore, the inhibition of its biosynthesis may provide a novel antiparasitic drug target. To identify a gene specifically required for RQ biosynthesis, we determined the complete genome sequence of a mutant strain of R. rubrum (F11), which cannot grow anaerobically and does not synthesize RQ, and compared it with that of a spontaneous revertant (RF111). RF111 can grow anaerobically and has recovered the ability to synthesize RQ. The two strains differ by a single base pair, which causes a nonsense mutation in the putative methyltransferase gene rquA. To test whether this mutation is important for the F11 phenotype, the wild-type rquA gene was cloned into the pRK404E1 vector and conjugated into F11. Complementation of the anaerobic growth defect in F11 was observed, and liquid chromatography-time of flight mass spectrometry (LC-TOF-MS) analysis of lipid extracts confirmed that plasmid-complemented F11 was able to synthesize RQ. To further validate the requirement of rquA for RQ biosynthesis, we generated a deletion mutant from wild-type R. rubrum by the targeted replacement of rquA with a gentamicin resistance cassette. The ΔrquA mutant exhibited the same phenotype as that of F11. These results are significant because rquA is the first gene to be discovered that is required for RQ biosynthesis.

Topics: Aerobiosis; Anaerobiosis; Biosynthetic Pathways; Chromatography, Liquid; Codon, Nonsense; DNA Mutational Analysis; DNA, Bacterial; Gene Deletion; Genetic Complementation Test; Genome, Bacterial; Humans; Mass Spectrometry; Methyltransferases; Molecular Sequence Data; Rhodospirillum rubrum; Sequence Analysis, DNA; Ubiquinone

Rhodoquinone (RQ) is an important cofactor used in the anaerobic energy metabolism of Rhodospirillum rubrum. RQ is structurally similar to ubiquinone (coenzyme Q or Q), a polyprenylated benzoquinone used in the aerobic respiratory chain. RQ is also found in several eukaryotic species that utilize a fumarate reductase pathway for anaerobic respiration, an important example being the parasitic helminths. RQ is not found in humans or other mammals, and therefore inhibition of its biosynthesis may provide a parasite-specific drug target. In this report, we describe several in vivo feeding experiments with R. rubrum used for the identification of RQ biosynthetic intermediates. Cultures of R. rubrum were grown in the presence of synthetic analogs of ubiquinone and the known Q biosynthetic precursors demethylubiquinone, demethoxyubiquinone, and demethyldemethoxyubiquinone, and assays were monitored for the formation of RQ(3). Data from time course experiments and S-adenosyl-l-methionine-dependent O-methyltransferase inhibition studies are discussed. Based on the results presented, we have demonstrated that Q is a required intermediate for the biosynthesis of RQ in R. rubrum.

Topics: Chromatography, Liquid; Mass Spectrometry; Models, Biological; Molecular Structure; Rhodospirillum rubrum; Ubiquinone

Alveolar echinococcosis, which is due to the massive growth of larval Echinococcus multilocularis, is a life-threatening parasitic zoonosis distributed widely across the northern hemisphere. Commercially available chemotherapeutic compounds have parasitostatic but not parasitocidal effects. Parasitic organisms use various energy metabolic pathways that differ greatly from those of their hosts and therefore could be promising targets for chemotherapy. The aim of this study was to characterize the mitochondrial respiratory chain of E. multilocularis, with the eventual goal of developing novel antiechinococcal compounds. Enzymatic analyses using enriched mitochondrial fractions from E. multilocularis protoscoleces revealed that the mitochondria exhibited NADH-fumarate reductase activity as the predominant enzyme activity, suggesting that the mitochondrial respiratory system of the parasite is highly adapted to anaerobic environments. High-performance liquid chromatography-mass spectrometry revealed that the primary quinone of the parasite mitochondria was rhodoquinone-10, which is commonly used as an electron mediator in anaerobic respiration by the NADH-fumarate reductase system of other eukaryotes. This also suggests that the mitochondria of E. multilocularis protoscoleces possess an anaerobic respiratory chain in which complex II of the parasite functions as a rhodoquinol-fumarate reductase. Furthermore, in vitro treatment assays using respiratory chain inhibitors against the NADH-quinone reductase activity of mitochondrial complex I demonstrated that they had a potent ability to kill protoscoleces. These results suggest that the mitochondrial respiratory chain of the parasite is a promising target for chemotherapy of alveolar echinococcosis.

Topics: Anaerobiosis; Animals; Echinococcosis, Hepatic; Echinococcus multilocularis; Electron Transport; Enzyme Inhibitors; Mitochondria; Nitro Compounds; Oxidoreductases Acting on CH-CH Group Donors; Quinazolines; Rotenone; Thiazoles; Ubiquinone

Rhodoquinone (RQ) participates in fumarate reduction under anaerobiosis in some bacteria and some primitive eukaryotes. Euglena gracilis, a facultative anaerobic protist, also possesses significant rhodoquinone-9 (RQ9) content. Growth under low oxygen concentration induced a decrease in cytochromes and ubiquinone-9 (UQ9) content, while RQ9 and fumarate reductase (FR) activity increased. However, in cells cultured under aerobic conditions, a relatively high RQ9 content was also attained together with significant FR activity. In addition, RQ9 purified from E. gracilis mitochondria was able to trigger the activities of cytochrome bc1 complex, bc1-like alternative component and alternative oxidase, although with lower efficiency (higher Km, lower Vm) than UQ9. Moreover, purified E. gracilis mitochondrial NAD+-independent D-lactate dehydrogenase (D-iLDH) showed preference for RQ9 as electron acceptor, whereas L-iLDH and succinate dehydrogenase preferred UQ9. These results indicated a physiological role for RQ9 under aerobiosis and microaerophilia in E. gracilis mitochondria, in which RQ9 mediates electron transfer between D-iLDH and other respiratory chain components, including FR.

Topics: Aerobiosis; Animals; Cell Respiration; Cytochromes c; Electron Transport; Euglena gracilis; Lactates; Mitochondria; Succinate Dehydrogenase; Ubiquinone

The components and organization of the respiratory chain in helminth mitochondria vary remarkably depending upon the stage of the life cycle. Mitochondrial complex I in the parasitic helminth Ascaris suum uses ubiquinone-9 (UQ(9)) and rhodoquinone-9 (RQ(9)) under aerobic and anaerobic conditions, respectively. In this study, we investigated structural features of the quinone reduction site of A. suum complex I using a series of quinazoline-type inhibitors and also by the kinetic analysis of rhodoquinone-2 (RQ(2)) and ubiquinone-2 (UQ(2)) reduction. Structure-activity profiles of the inhibition by quinazolines were comparable, but not completely identical, between NADH-RQ(2) and NADH-UQ(2) oxidoreductase activities. However, the inhibitory mechanism of quinazolines was competitive and partially competitive against RQ(2) and UQ(2), respectively. The pH profiles of both activities differed remarkably; NADH-RQ(2) oxidoreductase activity showed an optimum pH at 7.6, whereas NADH-UQ(2) oxidoreductase activity showed two optima pH at 6.4 and 7.2. Our results indicate that although A. suum complex I uses both RQ(2) and UQ(2) as an electron acceptor, the manner of reaction (or binding) of the two quinones differs.

Topics: Animals; Ascaris suum; Electron Transport Complex I; Enzyme Inhibitors; Hydrogen-Ion Concentration; Mitochondria; Quinazolines; Structure-Activity Relationship; Ubiquinone

Euglena gracilis cells grown under aerobic and anaerobic conditions were compared for their whole cell rhodoquinone and ubiquinone content and for major protein spots contained in isolated mitochondria as assayed by two-dimensional gel electrophoresis and mass spectrometry sequencing. Anaerobically grown cells had higher rhodoquinone levels than aerobically grown cells in agreement with earlier findings indicating the need for fumarate reductase activity in anaerobic wax ester fermentation in Euglena. Microsequencing revealed components of complex III and complex IV of the respiratory chain and the E1beta subunit of pyruvate dehydrogenase to be present in mitochondria of aerobically grown cells but lacking in mitochondria from anaerobically grown cells. No proteins were identified as specific to mitochondria from anaerobically grown cells. cDNAs for the E1alpha, E2, and E3 subunits of mitochondrial pyruvate dehydrogenase were cloned and shown to be differentially expressed under aerobic and anaerobic conditions. Their expression patterns differed from that of mitochondrial pyruvate:NADP(+) oxidoreductase, the N-terminal domain of which is pyruvate:ferredoxin oxidoreductase, an enzyme otherwise typical of hydrogenosomes, hydrogen-producing forms of mitochondria found among anaerobic protists. The Euglena mitochondrion is thus a long sought intermediate that unites biochemical properties of aerobic and anaerobic mitochondria and hydrogenosomes because it contains both pyruvate:ferredoxin oxidoreductase and rhodoquinone typical of hydrogenosomes and anaerobic mitochondria as well as pyruvate dehydrogenase and ubiquinone typical of aerobic mitochondria. Our data show that under aerobic conditions Euglena mitochondria are prepared for anaerobic function and furthermore suggest that the ancestor of mitochondria was a facultative anaerobe, segments of whose physiology have been preserved in the Euglena lineage.

Topics: Animals; Biochemistry; Cloning, Molecular; Databases as Topic; DNA, Complementary; Electron Transport; Electrophoresis, Gel, Two-Dimensional; Euglena gracilis; Expressed Sequence Tags; Gene Expression Regulation, Bacterial; Hydrogen; Mitochondria; Models, Chemical; Molecular Sequence Data; Oxygen; Peptides; Phylogeny; Protein Structure, Tertiary; Proteome; Pyruvic Acid; Trypsin; Ubiquinone

The long-lived mutant of Caenorhabditis elegans, clk-1, is unable to synthesize ubiquinone, CoQ(9). Instead, the mutant accumulates demethoxyubiquinone(9) and small amounts of rhodoquinone(9) as well as dietary CoQ(8). We found a profound defect in oxidative phosphorylation, a test of integrated mitochondrial function, in clk-1 mitochondria fueled by NADH-linked electron donors, i.e. complex I-dependent substrates. Electron transfer from complex I to complex III, which requires quinones, is severely depressed, whereas the individual complexes are fully active. In contrast, oxidative phosphorylation initiated through complex II, which also requires quinones, is completely normal. Here we show that complexes I and II differ in their ability to use the quinone pool in clk-1. This is the first direct demonstration of a differential interaction of complex I and complex II with the endogenous quinone pool. This study uses the combined power of molecular genetics and biochemistry to highlight the role of quinones in mitochondrial function and aging.

Topics: Animals; Ascorbic Acid; Caenorhabditis elegans; Electron Transport Complex I; Electron Transport Complex II; Glutamic Acid; Hydroquinones; Malates; Mitochondria; Mutation; Oxidative Phosphorylation; Pyruvic Acid; Quinones; Substrate Specificity; Tetramethylphenylenediamine; Time Factors; Ubiquinone

Infections with parasitic helminths are important causes of morbidity and mortality worldwide. New drugs that are parasite specific and minimally toxic to the host are needed to counter these infections effectively. Here we report the finding of a previously unidentified compound, nafuredin, from Aspergillus niger. Nafuredin inhibits NADH-fumarate reductase (complexes I + II) activity, a unique anaerobic electron transport system in helminth mitochondria, at nM order. It competes for the quinone-binding site in complex I and shows high selective toxicity to the helminth enzyme. Moreover, nafuredin exerts anthelmintic activity against Haemonchus contortus in in vivo trials with sheep. Thus, our study indicates that mitochondrial complex I is a promising target for chemotherapy, and nafuredin is a potential lead compound as an anthelmintic isolated from microorganisms.

Topics: Administration, Oral; Animals; Anthelmintics; Ascaris suum; Aspergillus niger; Electron Transport; Feces; Haemonchiasis; Haemonchus; Inhibitory Concentration 50; Kinetics; Mitochondria; Molecular Structure; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Pyrones; Sheep; Time Factors; Ubiquinone

Mutations in the clk-1 gene of the nematode Caenorhabditis elegans result in slowed development, sluggish adult behaviors, and an increased lifespan. CLK-1 is a mitochondrial polypeptide with sequence and functional conservation from human to yeast. Coq7p, the Saccharomyces cerevisiae homologue, is essential for ubiquinone (coenzyme Q or Q) synthesis and therefore respiration. However, based on assays of respiratory function, it has been reported that the primary defect in the C. elegans clk-1 mutants is not in Q biosynthesis. How do the clk-1 mutant worms have essentially normal rates of respiration, when biochemical studies in yeast suggest a Q deficiency? Nematodes are routinely fed Escherichia coli strains containing a rich supply of Q. To study the Q synthesized by C. elegans, we cultured worms on an E. coli mutant that lacks Q and found that clk-1 mutants display early developmental arrest from eggs, or sterility emerging from dauer stage. Provision of Q-replete E. coli rescues these defects. Lipid analysis showed that clk-1 worms lack the nematode Q(9) isoform and instead contain a large amount of a metabolite that is slightly more polar than Q(9). The clk-1 mutants also have increased levels of Q(8), the E. coli isoform, and rhodoquinone-9. These results show that the clk-1 mutations result in Q auxotrophy evident only when Q is removed from the diet, and that the aging and developmental phenotypes previously described are consistent with altered Q levels and distribution.

Topics: Aging; Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Culture Media; Diet; Escherichia coli; Glycolysis; Helminth Proteins; Humans; Infertility; Larva; Longevity; Mitochondria; Nutritional Requirements; Oxidative Phosphorylation; Protein Isoforms; Rats; Species Specificity; Stress, Physiological; Ubiquinone

A proton-activated electron transfer (PAET) mechanism, involving a protonated semiquinone intermediate state, had been proposed for the electron-transfer reaction k(2)AB [Q(A)(-)(*)Q(B)(-)(*) + H(+) <--> Q(A)(-)(*)(Q(B)H)(*) --> Q(A)(Q(B)H)(-)] in reaction centers (RCs) from Rhodobacter sphaeroides [Graige, M. S., Paddock, M. L., Bruce, M. L., Feher, G., and Okamura, M. Y. (1996) J. Am. Chem. Soc. 118, 9005-9016]. Confirmation of this mechanism by observing the protonated semiquinone (Q(B)H)(*) had not been possible, presumably because of its low pK(a). By replacing the native Q(10) in the Q(B) site with rhodoquinone (RQ), which has a higher pK(a), we were able to observe the (Q(B)H)(*) state. The pH dependence of the semiquinone optical spectrum gave a pK(a) = 7.3 +/- 0.2. At pH < pK(a), the observed rate for the reaction was constant and attributed to the intrinsic electron-transfer rate from Q(A)(-)(*) to the protonated semiquinone (i.e., k(2)AB = k(ET)(RQ) = 2 x 10(4) s(-)(1)). The rate decreased at pH > pK(a) as predicted by the PAET mechanism in which fast reversible proton transfer precedes rate-limiting electron transfer. Consequently, near pH 7, the proton-transfer rate k(H) >> 10(4) s(-)(1). Applying the two step mechanism to RCs containing native Q(10) and taking into account the change in redox potential, we find reasonable values for the fraction of (Q(B)H)(*) congruent with 0.1% (consistent with a pK(a)(Q(10)) of approximately 4.5) and k(ET)(Q(10)) congruent with 10(6) s(-)(1). These results confirm the PAET mechanism in RCs with RQ and give strong support that this mechanism is active in RCs with Q(10) as well.

Topics: Benzoquinones; Electron Transport; Hydrogen-Ion Concentration; Kinetics; Naphthoquinones; Oxidation-Reduction; Photolysis; Photosynthetic Reaction Center Complex Proteins; Proton-Motive Force; Protons; Rhodobacter sphaeroides; Spectrophotometry; Ubiquinone

The respiratory chain of Caenorhabditis elegans was characterized in mitochondria isolated from aerobically grown nematodes. Nematode mitochondria contain ubiquinone-9 as a major component and rhodoquinone-9 as a minor component. The ratio of ubiquinone-9/rhodoquinone-9 is higher in C. elegans mitochondria than in mitochondria from second-stage larvae of Ascaris suum, the free-living stage of porcine gut-dwelling nematode. The individual oxidoreductase activities comprising succinate oxidase and the amount of substrate-reducible cytochromes are comparable to those of mitochondria from second-stage larvae of A. suum. The specific activity of fumarate reductase is lower in C. elegans mitochondria than in mitochondria from second-stage larvae of A. suum, but still higher than in mammalian mitochondria. These results indicate that the free-living nematode C. elegans is capable of synthesizing rhodoquinone, as distinguished from aerobic mammalian species, although its mitochondria appear more aerobic than A. suum larval mitochondria.

Topics: Aerobiosis; Animals; Caenorhabditis elegans; Electron Transport; Mitochondria; Spectrophotometry; Succinate Dehydrogenase; Ubiquinone

Although schistosomes were thought to be one of the few parasitic helminths that do not produce succinate via fumarate reduction, it was recently demonstrated that sporocysts of Schistosoma mansoni produce, under certain conditions, succinate in addition to lactate. This succinate production was only observed when the respiratory chain activity of the sporocysts was inhibited, which suggested that succinate is produced by fumarate reduction. In this report the presence of essential components for fumarate reduction was investigated in various stages of S. mansoni and it was shown that, in contrast to adults, sporocysts contained a substantial amount of rhodoquinone which is essential for efficient fumarate reduction in eukaryotes. This rhodoquinone was not made by modification of ubiquinone obtained from the host, but was synthesized de novo. Furthermore, it was shown that complex II of the electron-transport chain in schistosomes has the kinetic properties of a dedicated fumarate reductase instead of those of a succinate dehydrogenase. The presence of such an enzyme, together with the substantial amounts of rhodoquinone, shows that in S. mansoni sporocysts succinate is produced via fumarate reduction. Therefore, the energy metabolism of schistosomes does not differ in principle from most other parasitic helminths, which are known to rely heavily on fumarate reduction.

Topics: Animals; Fumarates; Oxidation-Reduction; Schistosoma mansoni; Succinate Dehydrogenase; Succinic Acid; Ubiquinone

Most adult parasitic helminths have an anaerobic energy metabolism in which fumarate is reduced to succinate by fumarate reductase. Rhodoquinone (RQ) is an essential component of the electron transport associated with this fumarate reduction, whereas ubiquinone (UQ) is used in the aerobic energy metabolism of parasites. Not known yet, however, is the RQ and UQ composition during the entire life cycle nor the origin of RQ in parasitic helminths. This report demonstrates the essential function of RQ in anaerobic energy metabolism during the entire life cycle of Fasciola hepatica, as the amount of RQ present reflected the importance of fumarate reduction in various stages. We also studied the origin of RQ, as earlier studies on the protozoan Euglena gracilis suggested that RQ is synthesized from UQ. Therefore, in parasitic helminths RQ might be synthesized by modification of UQ obtained from the host. However, we demonstrated that in F. hepatica adults RQ was not produced by modification of UQ obtained from the host but that RQ was synthesized de novo, as (i) the chain-length of the quinones of F. hepatica adults was not related to the chain length of the quinone of the host, (ii) despite many attempts we could never detect any in vitro conversion of UQ9 into RQ9 or into UQ10, neither by intact adult flukes nor by homogenates of F. hepatica adults and (iii) F. hepatica adults used mevalonate as precursor for the synthesis of RQ. We also showed that the rate of quinone synthesis in F. hepatica adults was comparable to that in the free-living nematode Caenorhabditis elegans. These results prompted the suggestion that RQ is synthesized via a pathway nearly identical to that of UQ biosynthesis: possibly only the last reaction differs.

Topics: Animals; Caenorhabditis elegans; Cell Compartmentation; Energy Metabolism; Euglena gracilis; Fasciola hepatica; Mevalonic Acid; Subcellular Fractions; Ubiquinone

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 dehydrogenase-type complex II, but with the functional characteristics of the prokaryotic fumarate reductases.

Topics: Animals; Electron Transport; Electron Transport Complex II; Helminths; Kinetics; Multienzyme Complexes; Oxidation-Reduction; Oxidoreductases; Succinate Dehydrogenase; Ubiquinone

To elucidate the mechanism of anthelmintic action of bithionol, the inhibitory effect of the drug on NADH-fumarate reductase (NADH-FR) of Ascaris lumbricoides suum was examined. NADH-FR, an enzyme of anaerobic carbohydrate metabolic pathway was solubilized from the mitochondria of the worm's muscle with deoxycholate, and then partially purified with the monoethanolamine-Sepharose 4B column chromatography. Rhodoquinone (RQ), which is required for the electron transfer from NADH to fumarate, was separated from the enzyme protein and phospholipids. Although the enzyme protein fraction eluted from the above column did not show NADH-FR activity, this enzyme was reactivated by the addition of purified RQ and phosphatidylcholine. The IC50 value of bithionol for reconstituted NADH-FR was 18 +/- 2 microM. The inhibition type was competitive to RQ. Bithionol inhibited at most 30% NADH-ferricyanide reductase, which did not require RQ, even at high concentration of 150 microM. These results suggest that the pharmacological action of bithionol, a phenolic anthelmintic, depends on the inhibition of the electron transport system by the competition with RQ.

Topics: Animals; Ascaris; Bithionol; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Phospholipids; Ubiquinone

Electron-transfer flavoprotein:rhodoquinone oxidoreductase (ETF-RO) was purified to homogeneity from anaerobic mitochondria of the parasitic nematode, Ascaris suum. The enzyme has a subunit molecular mass of 64.5 kDa and is similar in many respects to the electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF-UO) characterized in mammalian tissues. EPR spectroscopy of the purified enzyme revealed signals at g = 2.076, 1,936, and 1.883, arising from an iron-sulfur center, as well as signals attributable to a flavin semiquinone. Potentiometric titration on the enzyme with dithionite yielded an oxidation-reduction midpoint potential (Em) for the iron-sulfur center of +25 mV at pH 7.4. The reduction of flavin occurred in two distinct steps, with a flavin semiquinone radical detected as an intermediate. The Em values for the two steps in the complete reduction of flavin were +15 mV and -9 mV, respectively. Physiologically, the ascarid ETF-RO accepts electrons from a low potential quinone, rhodoquinone, and functions in a direction opposite to that of the ETF-UO. Incubations of A. suum submitochondrial particles with NADH, 2-methylcrotonyl-CoA, purified A. suum electron-transfer flavoprotein and 2-methyl branched-chain enoyl-CoA reductase resulted in significant 2-methylbutyryl-CoA formation, which was inhibited by both rotenone and antisera to the purified ETF-RO. Quinone extraction of the submitchondrial particles with dry pentane resulted in almost the complete loss of 2-MBCoA formation by the system. However, the reincorporation of rhodoquinone, but not ubiquinone restored over 50% of the NADH-dependent 2-MBCoA formation.

Topics: Amino Acid Sequence; Amino Acids; Anaerobiosis; Animals; Antibodies; Ascaris suum; Cattle; Chromatography; Electron-Transferring Flavoproteins; Electrophoresis, Polyacrylamide Gel; Female; Flavoproteins; Macromolecular Substances; Male; Mitochondria, Heart; Mitochondria, Liver; Mitochondria, Muscle; Molecular Sequence Data; Molecular Weight; Multienzyme Complexes; Oxidoreductases; Potentiometry; Rabbits; Rats; Sequence Homology, Amino Acid; Spectrophotometry; Submitochondrial Particles; Swine; Ubiquinone

The Ascaris larval respiratory chain, particularly complex II (succinate-ubiquinone oxidoreductase), was characterized in isolated mitochondria. Low-temperature difference spectra showed the presence of substrate-reducible cytochromes aa3 of complex IV, c+c1 and b of complex III (ubiquinol-cytochrome c oxidoreductase) in mitochondria from second-stage larvae (L2 mitochondria). Quinone analysis by high-performance liquid chromatography showed that, unlike adult mitochondria, which contain only rhodoquinone-9, L2 mitochondria contain ubiquinone-9 as a major component. Complex II in L2 mitochondria was kinetically different from that in adult mitochondria. The individual oxidoreductase activities comprising succinate oxidase, and fumarate reductase were determined in mitochondria from L2 larvae, from larvae cultured to later stages, and from adult nematodes. The L2 mitochondria exhibited the highest specific activity of cytochrome c oxidase, indicating that L2 larvae have the most aerobic respiratory chain among the stages studied. The Cybs subunit of complex II in L2 and cultured-larvae mitochondria exhibited different reactivities against anti-adult Cybs antibodies. Taken together, these results indicate that the complex II of larvae is different from its adult counterpart. In parallel with this change in mitochondrial biogenesis, biosynthetic conversion of quinones occurs during development in Ascaris nematodes.

Topics: Animals; Ascaris suum; Cattle; Electron Transport Complex II; Fumarates; Larva; Mitochondria; Models, Biological; Multienzyme Complexes; Myocardium; NAD(P)H Dehydrogenase (Quinone); Oxidoreductases; Quinones; Succinate Dehydrogenase; Succinates; Succinic Acid; Ubiquinone

Nine Zoogloea strains including the type strain of Z. ramigera (IAM 12136 = ATCC 19544 = N.C. Dondero 106) and newly isolated strains were investigated for isoprenoid quinone composition and whole-cell fatty acid profiles. Seven of the tested strains, having phenotypic properties typical of Zoogloea, were characterized by their production of both ubiquinone-8 and rhodoquinone-8 as major quinones, whereas the remaining two strains, Z. ramigera IAM 12669 (= K. Crabtree I-16-M) and IAM 12670 (= P.R. Dugan 115), formed ubiquinone-10 and ubiquinone-8, respectively, as the sole quinone. All rhodoquinone-producing strains contained palmitoleic acid and 3-hydroxy-decanoic acid as the major components of nonpolar and hydroxylated fatty acids, respectively. Marked differences were noted in the fatty acid composition between the strains with and without rhodoquinones. The chemotaxonomic data suggested that the rhodoquinone-lacking strains should be excluded from the genus Zoogloea. Since there have been no reliable taxonomic tools for Zoogloea, rhodoquinone analysis may provide a new criterion of great promise for identifying Zoogloea strains.

Topics: Chromatography, High Pressure Liquid; Chromatography, Thin Layer; Culture Media; Decanoic Acids; Fatty Acids; Fatty Acids, Monounsaturated; Palmitic Acids; Quinones; Ubiquinone; Zoogloea

Complex II of the anaerobic respiratory chain in Ascaris muscle mitochondria showed a high fumarate reductase activity when reduced methyl viologen was used as the electron donor. The maximum activity was 49 mumol/min per mg protein, which is much higher than that of the mammalian counterpart. The mitochondria of Ascaris-fertilized eggs, which require oxygen for its development, also showed fumarate reductase activity with a specific activity intermediate between those of adult Ascaris and mammals. Antibody against the Ascaris flavoprotein subunit reacted with the mammalian counterparts, whereas those against the Ascaris iron-sulfur protein subunit did not crossreact, although the amino acid compositions of the subunits in Ascaris and bovine heart were quite similar. Cytochrome b-558 of Ascaris complex II was separated from flavoprotein and iron-sulphur protein subunits by high performance liquid chromatography with a gel permeation system in the presence of Sarkosyl. Isolated cytochrome b-558 is composed of two hydrophobic polypeptides with molecular masses of 17.2 and 12.5 kDa determined by gradient gel, which correspond to the two small subunits of complex II. Amino acid compositions of these small subunits showed little similarity with those of cytochrome b-560 of bovine heart complex II. NADH-fumarate reductase, which is the final enzyme complex in the anaerobic respiratory chain in Ascaris, was reconstituted with bovine heart complex I, Ascaris complex II and phospholipids. The maximum activity was 430 nmol/min per mg protein of complex II. Rhodoquinone was essential for this reconstitution, whereas ubiquinone showed no effect. The results clearly indicate the unique role of Ascaris complex II as fumarate reductase and the indispensability of rhodoquinone as the low-potential electron carrier in the NADH-fumarate reductase system.

Topics: Amino Acid Sequence; Animals; Ascaris; Cytochrome b Group; Electron Spin Resonance Spectroscopy; Electron Transport; Electron Transport Complex II; Electrophoresis, Polyacrylamide Gel; Escherichia coli; Hydrogen-Ion Concentration; Kinetics; Mitochondria; Molecular Sequence Data; Molecular Weight; Multienzyme Complexes; Muscles; NAD; NADPH Oxidases; Ovum; Oxidoreductases; Oxygen; Succinate Dehydrogenase; Ubiquinone

The occurrence of rhodoquinone as a mitochondrial membrane component was demonstrated in adult Hymenolepis diminuta. Chromatographic separation of pentane extracts, from lyophilized mitochondrial membranes, coupled with spectral analyses of separated material demonstrated the presence of rhodoquinone. The presence of ubiquinone was not apparent. Rhodoquinone content of membranes was about 1.2 micrograms (mg protein)-1. The rhodoquinone requirement of the H. diminuta electron transport system was demonstrated both in terms of the less active NADH oxidase and the physiologically required, NADH-dependent fumarate reductase employing lyophilized mitochondrial membranes as the source of activities. Pentane extraction of membranes virtually abolished the oxidase and fumarate reductase systems. Supplementation of pentane-treated membranes with H. diminuta rhodoquinone restored oxidase and fumarate reductase activities to levels simulating those of lyophilized membranes. Ubiquinone did not substitute for rhodoquinone. The rhodoquinone-reconstituted membranes displayed rotenone sensitivity. These findings represent the first direct demonstration of the rhodoquinone requirement of helminth electron transport-coupled oxidase and fumarate reductase.

Topics: Animals; Electron Transport; Hymenolepis; Intracellular Membranes; Mitochondria; Multienzyme Complexes; NADH, NADPH Oxidoreductases; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Oxygen Consumption; Peroxides; Succinates; Ubiquinone

Topics: Animals; Brugia; Dipetalonema; Dirofilaria immitis; Filarioidea; Onchocerca; Polyisoprenyl Phosphates; Terpenes; Ubiquinone

The role of rhodoquinone and ubiquinone in the oxygen photoreducing (photooxidase) activity of Rhodospirillum rubrum was investigated. The sole addition of purified rhodoquinone restored photooxidase activity in isolated chromatophores which had been extracted with organic solvents and which were apparently free of secondary acceptor ubiquinone. Rhodoquinone also enhanced photooxidase activity in photoreaction center preparations from which secondary ubiquinone seemed to have been removed. Those results suggest that rhodoquinone accepts electrons directly from primary ubiquinone during chromatophore photooxidase activity. In contrast, rhodoquinone does not participate in the basal activity of photoreaction center preparations, which seems to result from the autooxidation of both primary and secondary ubiquinone.

Topics: Bacterial Chromatophores; Bacterial Proteins; NADH, NADPH Oxidoreductases; Oxidation-Reduction; Photochemistry; Quinone Reductases; Rhodospirillum rubrum; Ubiquinone

Topics: Animals; Energy Metabolism; Fasciola; Hydrogen Peroxide; Isoenzymes; L-Lactate Dehydrogenase; Oxidoreductases; Ubiquinone

Ubiquinone-10 and rhodoquinone-10 were detected in stages of the life-cycle of a pseudophyllidean cestode, Spirometra mansonoides, by chromatographic, UV spectrophotometric, proton nuclear magnetic resonance spectrometric and electron impact mass spectrometric methods. Ubiquinone-10 was identified in 1-day-old eggs and coracidia, and rhodoquinone-10 in coracidia, plerocercoids and adult tapeworms. Tentative identification were also made of ubiquinone-10 in procercoids and rhodoquinone-10 in 10-day-old eggs. The roles of benzoquinones in helminth aerobic and anaerobic metabolism are discussed in relation to their distribution in stages of the S. mansonoides life-cycle.

Topics: Animals; Female; Ovum; Spirometra; Ubiquinone

Topics: Acetone; Amines; Animals; Ascaris; Coenzymes; Enzyme Activation; Mitochondria; Mitochondria, Liver; Quinones; Rats; Species Specificity; Structure-Activity Relationship; Succinate Dehydrogenase; Ubiquinone

Topics: Aldehydes; Benzaldehydes; Benzoates; Carbon Isotopes; Metabolism; Parabens; Phenylacetates; Quinones; Radiometry; Research; Rhodospirillum; Rhodospirillum rubrum; Spectrum Analysis; Ubiquinone

Topics: Chemical Phenomena; Chemistry; Coenzymes; Quinones; Research; Ubiquinone