scholarly journals Electron Flow and Energy Conservation in a Hydrogenotrophic Methanogen

2020 ◽  
Author(s):  
John [email protected] Leigh ◽  
Caroline Harwood
Keyword(s):  
Energy Conservation ◽  
Electron Flow ◽  
Hydrogenotrophic Methanogen

Artificial Energy Conservation in Bacterial Photosynthetic Electron Transport

1976 ◽  
Vol 31 (3-4) ◽  
pp. 152-156 ◽  
Author(s):  
Achim Trebst
Keyword(s):  
Electron Transport ◽  
Energy Conservation ◽  
Proton Pump ◽  
Redox Reaction ◽  
Electron Flow ◽  
Proton Translocation ◽  
Photosynthetic Electron Transport ◽  
Reaction Cycle ◽  
Atp Formation ◽  
Internal Electron

Abstract In photosynthesis of chloroplasts and bacterial chromatophores an induced artificial electron flow bypass may restore the inhibition of electron flow and of coupled ATP formation by two possible mechanisms. An artificial transmembrane electron flow bypass will lead to artificial energy conservation, when the redox reaction cycle of the added mediator across the membrane acts as proton pump. In an artificial internal electron flow bypass an inhibited native energy conservation may be reactivated; here an electron flow bypass induced by the mediator in the inside space restores the native proton translocation. The inhibition and the restoration of electron flow by antimycin, dibromothymoquinone and valinomycin is compared.

1,2,3-Thiadiazolyl-Pheny 1-Ureas, New Inhibitors of Photosynthetic and Respiratory Energy Conservation

1975 ◽  
Vol 30 (7-8) ◽  
pp. 505-510 ◽  
Author(s):  
G. Hauska ◽  
A. Trebst ◽  
C. Kötter ◽  
H. Schulz
Keyword(s):  
Energy Transfer ◽  
Energy Conservation ◽  
Electron Flow ◽  
Aromatic Rings ◽  
Urea Derivatives ◽  
Photosynthetic Electron Flow ◽  
Atp Formation ◽  
Effective Inhibition ◽  
High Concentrations ◽  
Isolated Chloroplasts

Abstract Substituted 1,2,3-thiadiazolyl-phenyl-ureas were found to be inhibitors of energy conservation in respiration and photosynthesis. The most effective dichlorophenylderivative uncouples ATP formation in isolated chloroplasts or mitochondria, at a concentration of about 2 and 9 μм respectively. At a certain concentration range the compounds also appear to be energy transfer inhibitors, similar to the well known inhibition by carbodiimides. The significance of the chemical relation of carbodiimides to ureas in the mode of action on energy transfer is discussed. The thiadiazolyl-phenyl-ureas are inhibitors of electron flow only at relatively high concentrations, pointing out that sterig hindrance by two large aromatic rings at both nitrogens of the urea moiety abolishes the highly effective inhibition of photosynthetic electron flow by substituted urea derivatives, like DCMU.

scholarly journals Non-haem iron and the dissociation of piericidin A sensitivity from site 1 energy conservation in mitochondria from Torulopsis utilis

1971 ◽  
Vol 124 (1) ◽  
pp. 135-151 ◽  
Author(s):  
R. A. Clegg ◽  
P. B. Garland
Keyword(s):  
Energy Conservation ◽  
Electron Flow ◽  
Iron Concentration ◽  
Normal Function ◽  
Aerobic Incubation ◽  
Submitochondrial Particles ◽  
Limited Growth ◽  
Iron Deficient ◽  
Haem Iron ◽  
Acid Labile

1. The aerobic incubation of iron-deficient Torulopsis utilis cells for 12h under non-growing conditions results in the recovery by mitochondria of the previously absent site 1 energy conservation and sensitivity to piericidin A. 2. The recovery of piericidin A sensitivity but not site 1 is prevented by the presence of cycloheximide (100μg/ml) in the medium used for aerobic incubation of the cells. Rotenone sensitivity behaved similarly. 3. Chloramphenicol, erythromycin and tetracycline were without effect on the recovery of site 1 and piericidin A sensitivity. 4. Inclusion of 59Fe in the growth medium can be used as the basis for a highly sensitive assay for non-haem iron. 5. Iron-limited growth of T. utilis lowers the concentration of both non-haem iron and acid-labile sulphide of submitochondrial particles by over 20-fold compared with the ‘normal’ situation with iron-supplemented glycerol-limited growth. 6. Increases in the non-haem iron and acid-labile sulphide concentrations of submitochondrial particles occur when site 1 and piericidin A sensitivity are recovered. The increase is approximately halved by the presence of cycloheximide. 7. The non-haem iron of T. utilis submitochondrial particles does not exchange with added iron. 8. Continuous culture of T. utilis at the transition between glycerol- and iron-limitation results in cells where mitochondria possess site 1 energy conservation but lack piericidin A sensitivity. 8. It is concluded, in contrast with widely held views to the opposite, that energy conservation at site 1 does not require electron flow to proceed through a piericidin A- or rotenone-sensitive route. 9. Restriction of the iron supplied to growing T. utilis to a concentration just above that required for growth limitation demonstrates that a 10- to 20-fold decrease of the ‘normal’ non-haem iron concentration of both cells and mitochondria is without effect on the growth yield per unit of carbon source. Submitochondrial particles prepared from such iron-restricted but otherwise functionally normal cells have a non-haem iron concentration of about 0.5–0.8ng-atom/mg of protein. It is concluded that the concentration of iron–sulphur protein required for normal function by the respiratory chain is close to the concentrations of cytochromes and flavoproteins.

scholarly journals The Rnf Complex Is an Energy-Coupled Transhydrogenase Essential To Reversibly Link Cellular NADH and Ferredoxin Pools in the AcetogenAcetobacterium woodii

2018 ◽  
Vol 200 (21) ◽  
Author(s):  
Lars Westphal ◽  
Anja Wiechmann ◽  
Jonathan Baker ◽  
Nigel P. Minton ◽  
Volker Müller
Keyword(s):  
Energy Conservation ◽  
Electron Flow ◽  
Low Energy ◽  
Main Function ◽  
Autotrophic Growth ◽  
Acetobacterium Woodii ◽  
Lactate Oxidation ◽  
Energy Substrates ◽  
Content Type ◽  
Respiratory Enzyme

ABSTRACTThe Rnf complex is a respiratory enzyme that catalyzes the oxidation of reduced ferredoxin to the reduction of NAD+, and the negative free energy change of this reaction is used to generate a transmembrane ion gradient. In one class of anaerobic acetogenic bacteria, the Rnf complex is believed to be essential for energy conservation and autotrophic growth. We describe here a methodology for markerless mutagenesis in the model bacterium of this class,Acetobacterium woodii, which enabled us to delete thernfgenes and to test theirin vivorole. Thernfmutant did not grow on H2plus CO2, nor did it produce acetate or ATP from H2plus CO2, and ferredoxin:NAD+oxidoreductase activity and Na+translocation were also completely lost, supporting the hypothesis that the Rnf complex is the only respiratory enzyme in this metabolism. Unexpectedly, the mutant also did not grow on low-energy substrates, such as ethanol or lactate. Oxidation of these substrates is not coupled to the reduction of ferredoxin but only of NAD+, and we speculated that the growth phenotype is caused by a loss of reduced ferredoxin, indispensable for biosynthesis and CO2reduction. The electron-bifurcating hydrogenase ofA. woodiireduces ferredoxin, and indeed, the addition of H2to the cultures restored growth on ethanol and lactate. This is consistent with the hypothesis that endergonic reduction of ferredoxin with NADH is driven by reverse electron transport catalyzed by the Rnf complex, which renders the Rnf complex essential also for growth on low-energy substrates.IMPORTANCEFerredoxin and NAD+are key electron carriers in anaerobic bacteria, but energetically, they are not equivalent, since the redox potential of ferredoxin is lower than that of the NADH/NAD+couple. We describe by mutant studies inAcetobacterium woodiithat the main function of Rnf is to energetically link cellular pools of ferredoxin and NAD+. When ferredoxin is greater than NADH, exergonic electron flow from ferredoxin to NAD+generates a chemiosmotic potential. This is essential for energy conservation during autotrophic growth. When NADH is greater than ferredoxin, Rnf works in reverse. This reaction is essential for growth on low-energy substrates to provide reduced ferredoxin, indispensable for biosynthesis and CO2reduction. Our studies put a new perspective on the cellular function of the membrane-bound ion-translocating Rnf complex widespread in bacteria.

scholarly journals Essential anaplerotic role for the energy-converting hydrogenase Eha in hydrogenotrophic methanogenesis

2012 ◽  
Vol 109 (38) ◽  
pp. 15473-15478 ◽  
Author(s):  
Thomas J. Lie ◽  
Kyle C. Costa ◽  
Boguslaw Lupa ◽  
Suresh Korpole ◽  
William B. Whitman ◽  
...  
Keyword(s):  
Energy Conservation ◽  
Alternative Hypothesis ◽  
Electron Flow ◽  
Methanogenic Archaea ◽  
Complete Model ◽  
Methanococcus Maripaludis ◽  
Hydrogenotrophic Methanogenesis ◽  
Energy Conserving ◽  
Energy Converting

Despite decades of study, electron flow and energy conservation in methanogenic Archaea are still not thoroughly understood. For methanogens without cytochromes, flavin-based electron bifurcation has been proposed as an essential energy-conserving mechanism that couples exergonic and endergonic reactions of methanogenesis. However, an alternative hypothesis posits that the energy-converting hydrogenase Eha provides a chemiosmosis-driven electron input to the endergonic reaction. In vivo evidence for both hypotheses is incomplete. By genetically eliminating all nonessential pathways of H2 metabolism in the model methanogen Methanococcus maripaludis and using formate as an additional electron donor, we isolate electron flow for methanogenesis from flux through Eha. We find that Eha does not function stoichiometrically for methanogenesis, implying that electron bifurcation must operate in vivo. We show that Eha is nevertheless essential, and a substoichiometric requirement for H2 suggests that its role is anaplerotic. Indeed, H2 via Eha stimulates methanogenesis from formate when intermediates are not otherwise replenished. These results fit the model for electron bifurcation, which renders the methanogenic pathway cyclic, and as such requires the replenishment of intermediates. Defining a role for Eha and verifying electron bifurcation provide a complete model of methanogenesis where all necessary electron inputs are accounted for.

Enhancement of Energy Conservation by Hill Reaction Inhibitors in Isolated Spinach (Spinacia oleracea) Chloroplast Fragments

Weed Science ◽  
1978 ◽  
Vol 26 (1) ◽  
pp. 84-89 ◽  
Author(s):  
G. J. Bethlenfalvay ◽  
P. A. Castelfranco
Keyword(s):  
Electron Transport ◽  
Energy Conservation ◽  
Spinacia Oleracea ◽  
Electron Flow ◽  
Proton Translocation ◽  
Cyclic Process ◽  
Hill Reaction ◽  
Acceptor Site ◽  
Cyclic Electron Transport ◽  
Site Of Action

The effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)], propanil (3′,4′-dichloropropionanilide), and dibromothymoquinone (DBMIB) (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) on proton translocation and photophosphorylation in isolated spinach (Spinacia oleracea L.) chloroplast fragments was investigated. In the absence of added cofactors, O2, or artificial electron acceptors, cyclic electron transport occurred, which was coupled to energy conservation. Under aerobic conditions O2 acted as the terminal acceptor in non-cyclic electron transport. Proton translocation and photophosphorylation in the cyclic process were enhanced by diuron, desmedipham, and propanil, while in the non-cyclic process they were inhibited by all three herbicides. DBMIB inhibited proton translocation and photophosphorylation in both processes. Proton translocation and its enhancement increased with increasing light intensities. The finding that the plastoquinone (PQ) antagonist DBMIB disrupted cyclic as well as noncyclic electron flow, while diuron enhanced the cyclic and inhibited the noncyclic process, indicated that the acceptor site for endogenously-cycling electrons must lie between the active site of diuron inhibition and PQ, The close similarity in the behavior of diuron, desmedipham, and propanil suggests that their site of action is the same.

Plastoquinones in photosynthesis

1978 ◽  
Vol 284 (1002) ◽  
pp. 591-599 ◽  
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Energy Conservation ◽  
Thylakoid Membrane ◽  
Electron Flow ◽  
Proton Translocation ◽  
Photosynthetic Electron Transport ◽  
Atp Formation ◽  
Electron Transport Chains

Several plastoquinones with different or modified side chains have been characterized in plant material: they are localized in the inner thylakoid membrane of the chloroplast. So far only plastoquinone-45 (PQ-45) has been identified as an obligatory functional component of the photosynthetic electron transport chain in chloroplasts between photosystem II and photosystem I. A special form (semiquinone) of PQ-45 acts as primary acceptor Q of photosystem II, a large pool of PQ-45 as electron buffer, interconnecting several electron transport chains. The rôle of PQ, in energy conservation (ATP formation) is of particular current interest. Owing to vectorial electron flow across the thylakoid membrane, plastoquinone is thought to be reduced on the outside and plastohydroquinone to be oxidized on the inside of the membrane. This results in a proton translocation across the membrane and a build-up of a proton motive force which drives ATP formation. Old and new plastoquinone antagonists are described and the relevance of inhibitor studies on the rôle of plastoquinone in electron flow and photophosphorylation is discussed. Open questions and current problems of the mechanism of plastoquinone/plastoquinol transport across the membrane - and of proton translocation connected to it - relevant for the mechanism of energy conservation in photosynthesis, are pointed out.

scholarly journals A comparison of mitochondria from Torulopsis utilis grown in continous culture with glycerol, iron, ammonium, magnesium or phosphate as the growth-limiting nutrient

1971 ◽  
Vol 124 (1) ◽  
pp. 123-134 ◽  
Author(s):  
P. A Light ◽  
P. B. Garland
Keyword(s):  
Energy Conservation ◽  
Electron Flow ◽  
Respiratory Control ◽  
Indirect Evidence ◽  
Iron Limitation ◽  
Limited Growth ◽  
Respiratory Inhibitor ◽  
Limiting Nutrient ◽  
Haem Iron

1. Mitochondria prepared from Torulopsis utilis grown in a chemostat with iron-limited growth were found to lack energy conservation but not electron flow in that segment of the respiratory chain leading from intramitochondrial NADH to the cytochromes [i.e. the site 1 segment (Lehninger, 1964)]. 2. Site 1 energy conservation was present in mitochondria prepared from cells grown under conditions of limitation by glycerol, ammonium and magnesium. Phosphate-limited growth resulted in mitochondrial preparations without respiratory control. 3. Mitochondria from cells grown under conditions of iron limitation were insensitive to the respiratory inhibitor piericidin A, whereas sensitivity was present in mitochondria prepared from glycerol-, ammonium-, magnesium- or phosphate-limited cells. 4. These observations are considered to provide indirect evidence for a role of non-haem iron in the mechanism of energy conservation and also piericidin A sensitivity in T. utilis mitochondria. 5. A readily constructed and inexpensive pH-measuring and -controlling circuit is described for use with continuous-culture apparatus.

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