Energy-converting hydrogenases: the link between H2 metabolism and energy conservation

2019 ◽  
Vol 77 (8) ◽  
pp. 1461-1481 ◽  
Author(s):  
Marie Charlotte Schoelmerich ◽  
Volker Müller
Keyword(s):  
Energy Conservation ◽  
H2 Metabolism ◽  
Energy Converting

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.

scholarly journals Energy conservation by a hydrogenase-dependent chemiosmotic mechanism in an ancient metabolic pathway

2019 ◽  
Vol 116 (13) ◽  
pp. 6329-6334 ◽  
Author(s):  
Marie Charlotte Schoelmerich ◽  
Volker Müller
Keyword(s):  
Energy Conservation ◽  
Atp Synthase ◽  
Membrane Vesicles ◽  
Resting Cells ◽  
Respiratory Enzyme ◽  
Acetyl Coa Pathway ◽  
Acetogenic Bacterium ◽  
Genome Analyses ◽  
Chemiosmotic Coupling ◽  
Energy Converting

The ancient reductive acetyl-CoA pathway is employed by acetogenic bacteria to form acetate from inorganic energy sources. Since the central pathway does not gain net ATP by substrate-level phosphorylation, chemolithoautotrophic growth relies on the additional formation of ATP via a chemiosmotic mechanism. Genome analyses indicated that some acetogens only have an energy-converting, ion-translocating hydrogenase (Ech) as a potential respiratory enzyme. Although the Ech-encoding genes are widely distributed in nature, the proposed function of Ech as an ion-translocating chemiosmotic coupling site has neither been demonstrated in bacteria nor has it been demonstrated that it can be the only energetic coupling sites in microorganisms that depend on a chemiosmotic mechanism for energy conservation. Here, we show that the Ech complex of the thermophilic acetogenic bacteriumThermoanaerobacter kivuiis indeed a respiratory enzyme. Experiments with resting cells prepared fromT. kivuicultures grown on carbon monoxide (CO) revealed CO oxidation coupled to H2formation and the generation of a transmembrane electrochemical ion gradient (Δµ∼ion). Inverted membrane vesicles (IMVs) prepared from CO-grown cells also produced H2and ATP from CO (via a loosely attached CO dehydrogenase) or a chemical reductant. Finally, we show that Ech activity led to the translocation of both H+and Na+across the membrane of the IMVs. The H+gradient was then used by the ATP synthase for energy conservation. These data demonstrate that the energy-converting hydrogenase in concert with an ATP synthase may be the simplest form of respiration; it combines carbon dioxide fixation with the synthesis of ATP in an ancient pathway.

Habits, hardware, and energy conservation.

1981 ◽  
Vol 36 (4) ◽  
pp. 426-428 ◽  
Author(s):  
Paul C. Stern ◽  
Gerald T. Gardner
Keyword(s):  
Energy Conservation

Impact of roof shading on building energy performance in warm & humid climatic places of India

2020 ◽  
pp. 50-64
Author(s):  
Kuladeep Kumar Sadevi ◽  
Avlokita Agrawal
Keyword(s):  
Energy Consumption ◽  
Energy Conservation ◽  
Energy Performance ◽  
General Assumption ◽  
Climatic Conditions ◽  
Building Envelope ◽  
Passive Cooling ◽  
Base Case ◽  
U Value ◽  
The Impact

With the rise in awareness of energy efficient buildings and adoption of mandatory energy conservation codes across the globe, significant change is being observed in the way the buildings are designed. With the launch of Energy Conservation Building Code (ECBC) in India, climate responsive designs and passive cooling techniques are being explored increasingly in building designs. Of all the building envelope components, roof surface has been identified as the most significant with respect to the heat gain due to the incident solar radiation on buildings, especially in tropical climatic conditions. Since ECBC specifies stringent U-Values for roof assembly, use of insulating materials is becoming popular. Along with insulation, the shading of the roof is also observed to be an important strategy for improving thermal performance of the building, especially in Warm and humid climatic conditions. This study intends to assess the impact of roof shading on building’s energy performance in comparison to that of exposed roof with insulation. A typical office building with specific geometry and schedules has been identified as base case model for this study. This building is simulated using energy modelling software ‘Design Builder’ with base case parameters as prescribed in ECBC. Further, the same building has been simulated parametrically adjusting the amount of roof insulation and roof shading simultaneously. The overall energy consumption and the envelope performance of the top floor are extracted for analysis. The results indicate that the roof shading is an effective passive cooling strategy for both naturally ventilated and air conditioned buildings in Warm and humid climates of India. It is also observed that a fully shaded roof outperforms the insulated roof as per ECBC prescription. Provision of shading over roof reduces the annual energy consumption of building in case of both insulated and uninsulated roofs. However, the impact is higher for uninsulated roofs (U-Value of 3.933 W/m2K), being 4.18% as compared to 0.59% for insulated roofs (U-Value of 0.33 W/m2K).While the general assumption is that roof insulation helps in reducing the energy consumption in tropical buildings, it is observed to be the other way when insulation is provided with roof shading. It is due to restricted heat loss during night.

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