scholarly journals The Rnf complex is a Na+ coupled respiratory enzyme in a fermenting bacterium, Thermotoga maritima

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Martin Kuhns ◽  
Dragan Trifunović ◽  
Harald Huber ◽  
Volker Müller
Keyword(s):  
Electron Transport ◽  
Ion Transport ◽  
Cytoplasmic Membrane ◽  
Thermotoga Maritima ◽  
Physiological Role ◽  
Thermophilic Bacterium ◽  
Respiratory Enzyme ◽  
Membrane Bound ◽  
Reverse Electron Transport

Abstractrnf genes are widespread in bacteria and biochemical and genetic data are in line with the hypothesis that they encode a membrane-bound enzyme that oxidizes reduced ferredoxin and reduces NAD and vice versa, coupled to ion transport across the cytoplasmic membrane. The Rnf complex is of critical importance in many bacteria for energy conservation but also for reverse electron transport to drive ferredoxin reduction. However, the enzyme has never been purified and thus, ion transport could not be demonstrated yet. Here, we have purified the Rnf complex from the anaerobic, fermenting thermophilic bacterium Thermotoga maritima and show that is a primary Na+ pump. These studies provide the proof that the Rnf complex is indeed an ion (Na+) translocating, respiratory enzyme. Together with a Na+-F1FO ATP synthase it builds a simple, two-limb respiratory chain in T. maritima. The physiological role of electron transport phosphorylation in a fermenting bacterium is discussed.

scholarly journals Histochemical identification of the vascular endothelial isoenzyme of alkaline phosphatase.

1989 ◽  
Vol 37 (12) ◽  
pp. 1893-1898 ◽  
Author(s):  
H F Zoellner ◽  
N Hunter
Keyword(s):  
Alkaline Phosphatase ◽  
Physiological Role ◽  
Freeze Substitution ◽  
Differential Sensitivity ◽  
Rat Tissues ◽  
Microvascular Endothelium ◽  
Membrane Bound ◽  
Specific Inhibitors

Alkaline phosphatase (AP) is a widely studied membrane bound ecto-enzyme with an extensive distribution in nature. Three major human isoenzymes have been defined and can be distinguished on the basis of their differential sensitivity to specific inhibitors. Despite the voluminous literature describing AP, the physiological role of this enzyme is unclear. Microvascular endothelium is strongly AP positive and may provide a convenient model for study of the role of AP in vitro. This report describes the use of freeze-substitution and high-resolution plastic embedding techniques to identify the isoenzyme of endothelial AP by quantitative analysis of the relative inhibition by specific inhibitors of AP, using human gingival tissues and a number of rat tissues. Endothelial AP is found to be the liver/bone/kidney isoenzyme, indicating kidney as a credible source of enzyme for further experimental work investigating the role of AP.

scholarly journals Energy Conservation by the H2:Heterodisulfide Oxidoreductase from Methanosarcina mazei Gö1: Identification of Two Proton-Translocating Segments

1999 ◽  
Vol 181 (13) ◽  
pp. 4076-4080 ◽  
Author(s):  
Tina Ide ◽  
Sebastian Bäumer ◽  
Uwe Deppenmeier
Keyword(s):  
Electron Transport ◽  
Atp Synthase ◽  
Cytoplasmic Membrane ◽  
Respiratory Control ◽  
Atp Synthesis ◽  
Heterodisulfide Reductase ◽  
Methanosarcina Mazei ◽  
Energy Conserving ◽  
Membrane Bound ◽  
Synthase Inhibitor

ABSTRACT The membrane-bound H2:heterodisulfide oxidoreductase system of the methanogenic archaeon Methanosarcina mazeiGö1 catalyzed the H2-dependent reduction of 2-hydroxyphenazine and the dihydro-2-hydroxyphenazine-dependent reduction of the heterodisulfide of HS-CoM and HS-CoB (CoM-S-S-CoB). Washed inverted vesicles of this organism were found to couple both processes with the transfer of protons across the cytoplasmic membrane. The maximal H+/2e− ratio was 0.9 for each reaction. The electrochemical proton gradient (ΔμH+ ) thereby generated was shown to drive ATP synthesis from ADP plus Pi, exhibiting stoichiometries of 0.25 ATP synthesized per two electrons transported for both partial reactions. ATP synthesis and the generation of ΔμH+ were abolished by the uncoupler 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF 6847). The ATP synthase inhibitorN,N′-dicyclohexylcarbodiimide did not affect H+ translocation but led to an almost complete inhibition of ATP synthesis and decreased the electron transport rates. The latter effect was relieved by the addition of SF 6847. Thus, the energy-conserving systems showed a stringent coupling which resembles the phenomenon of respiratory control. The results indicate that two different proton-translocating segments are present in the H2:heterodisulfide oxidoreductase system; the first involves the 2-hydroxyphenazine-dependent hydrogenase, and the second involves the heterodisulfide reductase.

scholarly journals Flexibility in photosynthetic electron transport: The physiological role of plastoquinol terminal oxidase (PTOX)

2011 ◽  
Vol 1807 (8) ◽  
pp. 954-967 ◽  
Author(s):  
Allison E. McDonald ◽  
Alex G. Ivanov ◽  
Rainer Bode ◽  
Denis P. Maxwell ◽  
Steven R. Rodermel ◽  
...  
Keyword(s):  
Electron Transport ◽  
Physiological Role ◽  
Photosynthetic Electron Transport ◽  
Terminal Oxidase

scholarly journals Ae4 (Slc4a9) is an electroneutral monovalent cation-dependent Cl−/HCO3− exchanger

2016 ◽  
Vol 147 (5) ◽  
pp. 423-436 ◽  
Author(s):  
Gaspar Peña-Münzenmayer ◽  
Alvin T. George ◽  
Gary E. Shull ◽  
James E. Melvin ◽  
Marcelo A. Catalán
Keyword(s):  
Ion Transport ◽  
Physiological Role ◽  
Acinar Cells ◽  
Monovalent Cation ◽  
Ion Concentration ◽  
Secretory Cells ◽  
Whole Cell ◽  
Na Ions ◽  
Whole Cell Recordings

Ae4 (Slc4a9) belongs to the Slc4a family of Cl−/HCO3− exchangers and Na+-HCO3− cotransporters, but its ion transport cycle is poorly understood. In this study, we find that native Ae4 activity in mouse salivary gland acinar cells supports Na+-dependent Cl−/HCO3− exchange that is comparable with that obtained upon heterologous expression of mouse Ae4 and human AE4 in CHO-K1 cells. Additionally, whole cell recordings and ion concentration measurements demonstrate that Na+ is transported by Ae4 in the same direction as HCO3− (and opposite to that of Cl−) and that ion transport is not associated with changes in membrane potential. We also find that Ae4 can mediate Na+-HCO3− cotransport–like activity under Cl−-free conditions. However, whole cell recordings show that this apparent Na+-HCO3− cotransport activity is in fact electroneutral HCO3−/Na+-HCO3− exchange. Although the Ae4 anion exchanger is thought to regulate intracellular Cl− concentration in exocrine gland acinar cells, our thermodynamic calculations predict that the intracellular Na+, Cl−, and HCO3− concentrations required for Ae4-mediated Cl− influx differ markedly from those reported for acinar secretory cells at rest or under sustained stimulation. Given that K+ ions share many properties with Na+ ions and reach intracellular concentrations of 140–150 mM (essentially the same as extracellular [Na+]), we hypothesize that Ae4 could mediate K+-dependent Cl−/HCO3− exchange. Indeed, we find that Ae4 mediates Cl−/HCO3− exchange activity in the presence of K+ as well as Cs+, Li+, and Rb+. In summary, our results strongly suggest that Ae4 is an electroneutral Cl−/nonselective cation–HCO3− exchanger. We postulate that the physiological role of Ae4 in secretory cells is to promote Cl− influx in exchange for K+(Na+) and HCO3− ions.

scholarly journals Complex effects of pH on ROS from mitochondrial complex II driven complex I reverse electron transport challenge its role in tissue reperfusion injury

2020 ◽  
Author(s):  
Alexander S. Milliken ◽  
Chaitanya A. Kulkarni ◽  
Paul S. Brookes
Keyword(s):  
Electron Transport ◽  
Complex I ◽  
Ischemia Reperfusion ◽  
Mitochondrial Complex ◽  
Complex Ii ◽  
Effects Of Ph ◽  
Cellular Necrosis ◽  
Reverse Electron Transport ◽  
The Impact

ABSTRACTGeneration of mitochondrial reactive oxygen species (ROS) is an important process in triggering cellular necrosis and tissue infarction during ischemia-reperfusion (IR) injury. Ischemia results in accumulation of the metabolite succinate. Rapid oxidation of this succinate by mitochondrial complex II (Cx-II) during reperfusion reduces the co-enzyme Q (Co-Q) pool, thereby driving electrons backward into complex-I (Cx-I), a process known as reverse electron transport (RET), which is thought to be a major source of ROS. During ischemia, enhanced glycolysis results in an acidic cellular pH at the onset of reperfusion. While the process of RET within Cx-I is known to be enhanced by a high mitochondrial trans-membrane ΔpH, the impact of pH itself on the integrated process of Cx-II to Cx-I RET has not been fully studied. Using isolated mitochondria under conditions which mimic the onset of reperfusion (i.e., high [ADP]). We show that mitochondrial respiration (state 2 and state 3) as well as isolated Cx-II activity are impaired at acidic pH, whereas the overall generation of ROS by Cx-II to Cx-I RET was insensitive to pH. Together these data indicate that the acceleration of Cx-I RET ROS by ΔpH appears to be cancelled out by the impact of pH on the source of electrons, i.e. Cx-II. Implications for the role of Cx-II to Cx-I RET derived ROS in IR injury are discussed.

Physiological role of GlpB of anaerobic glycerol-3-phosphate dehydrogenase ofEscherichia coli

1995 ◽  
Vol 73 (3-4) ◽  
pp. 147-153 ◽  
Author(s):  
Monica E. R. Varga ◽  
Joel H. Weiner
Keyword(s):  
Escherichia Coli ◽  
Physiological Role ◽  
Anaerobic Growth ◽  
Paramagnetic Resonance ◽  
Terminal Electron Acceptor ◽  
Iron Sulfur Center ◽  
Anaerobic Electron Transport ◽  
Membrane Bound ◽  
Glycerol 3 Phosphate Dehydrogenase

Anaerobic sn-glycerol-3-phosphate dehydrogenase of Escherichia coli is encoded by an operon of three genes, glpACB. The promoter distal gene, glpB, encodes a 44-kilodalton polypeptide that is not part of the purified soluble dehydrogenase. By recombinant plasmid complementation, in a strain harboring a chromosomal deletion of glpACB, we found that all three genes were essential for anaerobic growth on glycerol-3-phosphate (G3P). By isolation of inner membrane preparations we confirmed the cytoplasmic membrane localization of GlpB. GlpB displayed an electron paramagnetic resonance spectrum that suggested the presence of iron–sulfur center(s) within GlpB. We used this spectrum to show that the center(s) were reduced by the artificial reductant dithionite and by the physiological substrate G3P but not by lactate or formate. The center(s) were oxidized by fumarate. These data indicated that GlpB mediates electron transfer from the soluble GlpAC dimer to the terminal electron acceptor fumarate via the membrane-bound menaquinone pool.Key words: glycerol-3-phosphate dehydrogenase, anaerobic electron transport, membrane proteins, ferredoxin, Escherichia coli.

Sign in / Sign up

Export Citation Format

Share Document