Chemical Genetics Analysis of an Aniline Mustard Anticancer Agent Reveals Complex I of the Electron Transport Chain as a Target

The inner mitochondrial membrane is selectively permeable, which limits the transport of solutes and metabolites across the membrane. This constitutes a problem when intramitochondrial enzymes are studied. The channel-forming antibiotic AlaM (alamethicin) was used as a potentially less invasive method to permeabilize mitochondria and study the highly branched electron-transport chain in potato tuber (Solanum tuberosum) and pea leaf (Pisum sativum) mitochondria. We show that AlaM permeabilized the inner membrane of plant mitochondria to NAD(P)H, allowing the quantification of internal NAD(P)H dehydrogenases as well as matrix enzymes in situ. AlaM was found to inhibit the electron-transport chain at the external Ca2+-dependent rotenone-insensitive NADH dehydrogenase and around complexes III and IV. Nevertheless, under optimal conditions, especially complex I-mediated NADH oxidation in AlaM-treated mitochondria was much higher than what has been previously measured by other techniques. Our results also show a difference in substrate specificities for complex I in mitochondria as compared with inside-out submitochondrial particles. AlaM facilitated the passage of cofactors to and from the mitochondrial matrix and allowed the determination of NAD+ requirements of malate oxidation in situ. In summary, we conclude that AlaM provides the best method for quantifying NADH dehydrogenase activities and that AlaM will prove to be an important method to study enzymes under conditions that resemble their native environment not only in plant mitochondria but also in other membrane-enclosed compartments, such as intact cells, chloroplasts and peroxisomes.

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Abstract P310: Mitochondrial Electron Transport Chain Dysfunction Is Associated With Mg Deficiency Induced Diastolic Dysfunction

Circulation Research ◽

10.1161/res.129.suppl_1.p310 ◽

2021 ◽

Vol 129 (Suppl_1) ◽

Author(s):

Man Liu ◽

Hong Liu ◽

Richard T Clements ◽

Feng Feng ◽

Jin O-Uchi ◽

...

Keyword(s):

Heart Failure ◽

Electron Transport ◽

Diastolic Dysfunction ◽

Mitochondrial Function ◽

Complex I ◽

Electron Transport Chain ◽

Diastolic Heart Failure ◽

Mg Deficiency ◽

Transport Chain ◽

Mg Content

Introduction: The prevalence of heart failure with preserved ejection fraction (HFpEF) is increasing, although there is no specific treatment for HFpEF yet because of poor understanding of the underlying pathophysiology. Our previous studies show that hypomagnesemia contributes to diastolic dysfunction and HFpEF by regulation of mitochondrial function and that Mg supplementation improves diastolic function. In this study, we investigated how mitochondria were affected by Mg deficiency. Methods: C57BL/6J mice were fed with a low-Mg diet (HypoMg mice, 15-30 mg/kg Mg) or a normal Mg diet (control mice, 600 mg/kg Mg) for 6 weeks. Mg repletion was achieved by feeding HypoMg mice with normal diet for another 6 weeks. Results: HypoMg mice showed significantly decreased serum Mg (0.38±0.03 mM vs. 1.14±0.03 mM of control, P<0.0001), diastolic dysfunction (E/e’=21.1±1.1 vs. 15.4±0.4 of control, P=0.011), increased mitochondrial ROS (1.9±0.2-fold of control, P<0.0001), decreased total mitochondrial Mg content (3.6±1.8 vs. 18.3±4.7 μM total Mg/mg mitochondrial protein of control, P=0.019), decreased ATP production in hearts (1.2±0.2 vs. 2.7±0.2 μmol/g heart tissue of control, P=0.0002), decreased complex I activity (ΔOCR NADH-rotenone =0.27±0.10 vs. 1.02±0.04 of control, P=0.0004 measured with Seahorse), and decreased complex I protein levels (50.2% reduction compared with control mice, P=0.009). Mg repletion reversed all these changes. Conclusion: HypoMg-induced diastolic dysfunction likely results from HypoMg-induced electron transport chain dysfunction resulting from a decrease in mitochondrial Mg content. Mg repletion reverses these changes, reinforcing the known correlation of increased Mg intake and reduced heart failure symptoms. In deficiency states, Mg supplementation may represent a novel treatment for diastolic heart failure by improving mitochondrial function.

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Tracking Electron Uptake from a Cathode into Shewanella Cells: Implications for Energy Acquisition from Solid-Substrate Electron Donors

mBio ◽

10.1128/mbio.02203-17 ◽

2018 ◽

Vol 9 (1) ◽

Cited By ~ 43

Author(s):

Annette R. Rowe ◽

Pournami Rajeev ◽

Abhiney Jain ◽

Sahand Pirbadian ◽

Akihiro Okamoto ◽

...

Keyword(s):

Electron Transfer ◽

Electron Transport ◽

Complex I ◽

Electron Transport Chain ◽

Electron Flow ◽

Extracellular Electron Transfer ◽

Terminal Electron Acceptor ◽

Cellular Energy ◽

Transport Chain ◽

Energy Acquisition

ABSTRACTWhile typically investigated as a microorganism capable of extracellular electron transfer to minerals or anodes,Shewanella oneidensisMR-1 can also facilitate electron flow from a cathode to terminal electron acceptors, such as fumarate or oxygen, thereby providing a model system for a process that has significant environmental and technological implications. This work demonstrates that cathodic electrons enter the electron transport chain ofS. oneidensiswhen oxygen is used as the terminal electron acceptor. The effect of electron transport chain inhibitors suggested that a proton gradient is generated during cathode oxidation, consistent with the higher cellular ATP levels measured in cathode-respiring cells than in controls. Cathode oxidation also correlated with an increase in the cellular redox (NADH/FMNH2) pool determined with a bioluminescence assay, a proton uncoupler, and a mutant of proton-pumping NADH oxidase complex I. This work suggested that the generation of NADH/FMNH2under cathodic conditions was linked to reverse electron flow mediated by complex I. A decrease in cathodic electron uptake was observed in various mutant strains, including those lacking the extracellular electron transfer components necessary for anodic-current generation. While no cell growth was observed under these conditions, here we show that cathode oxidation is linked to cellular energy acquisition, resulting in a quantifiable reduction in the cellular decay rate. This work highlights a potential mechanism for cell survival and/or persistence on cathodes, which might extend to environments where growth and division are severely limited.IMPORTANCEThe majority of our knowledge of the physiology of extracellular electron transfer derives from studies of electrons moving to the exterior of the cell. The physiological mechanisms and/or consequences of the reverse processes are largely uncharacterized. This report demonstrates that when coupled to oxygen reduction, electrode oxidation can result in cellular energy acquisition. This respiratory process has potentially important implications for how microorganisms persist in energy-limited environments, such as reduced sediments under changing redox conditions. From an applied perspective, this work has important implications for microbially catalyzed processes on electrodes, particularly with regard to understanding models of cellular conversion of electrons from cathodes to microbially synthesized products.

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