Electrocatalytic reduction of nitrate and selenate by NapAB

2011 ◽  
Vol 39 (1) ◽  
pp. 236-242 ◽  
Author(s):  
Andrew J. Gates ◽  
Clive S. Butler ◽  
David J. Richardson ◽  
Julea N. Butt
Keyword(s):  
Cytoplasmic Membrane ◽  
Current Knowledge ◽  
Reductase Activity ◽  
Protonmotive Force ◽  
Metabolic Diversity ◽  
Protein Film ◽  
Carbon Substrates ◽  
Redox Poise ◽  
Paracoccus Pantotrophus ◽  
High Level

Bacterial cellular metabolism is renowned for its metabolic diversity and adaptability. However, certain environments present particular challenges. Aerobic metabolism of highly reduced carbon substrates by soil bacteria such as Paracoccus pantotrophus presents one such challenge since it may result in excessive electron delivery to the respiratory redox chain when compared with the availability of terminal oxidant, O2. The level of a periplasmic ubiquinol-dependent nitrate reductase, NAP, is up-regulated in the presence of highly reduced carbon substrates. NAP oxidizes ubiquinol at the periplasmic face of the cytoplasmic membrane and reduces nitrate in the periplasm. Thus its activity counteracts the accumulation of excess reducing equivalents in ubiquinol, thereby maintaining the redox poise of the ubiquinone/ubiquinol pool without contributing to the protonmotive force across the cytoplasmic membrane. Although P. pantotrophus NapAB shows a high level of substrate specificity towards nitrate, the enzyme has also been reported to reduce selenate in spectrophotometric solution assays. This transaction draws on our current knowledge concerning the bacterial respiratory nitrate reductases and extends the application of PFE (protein film electrochemistry) to resolve and quantify the selenate reductase activity of NapAB.

Voltammetric characterization of the aerobic energy-dissipating nitrate reductase of Paracoccus pantotrophus: exploring the activity of a redox-balancing enzyme as a function of electrochemical potential

2007 ◽  
Vol 409 (1) ◽  
pp. 159-168 ◽  
Author(s):  
Andrew J. Gates ◽  
David J. Richardson ◽  
Julea N. Butt
Keyword(s):  
Nitrate Reductase ◽  
Nitrate Reduction ◽  
Reductase Activity ◽  
Electrochemical Potential ◽  
Intact Cells ◽  
Protein Film ◽  
Protein Film Voltammetry ◽  
Voltammetric Studies ◽  
Paracoccus Pantotrophus

Paracoccus pantotrophus expresses two nitrate reductases associated with respiratory electron transport, termed NapABC and NarGHI. Both enzymes derive electrons from ubiquinol to reduce nitrate to nitrite. However, while NarGHI harnesses the energy of the quinol/nitrate couple to generate a transmembrane proton gradient, NapABC dissipates the energy associated with these reducing equivalents. In the present paper we explore the nitrate reductase activity of purified NapAB as a function of electrochemical potential, substrate concentration and pH using protein film voltammetry. Nitrate reduction by NapAB is shown to occur at potentials below approx. 0.1 V at pH 7. These are lower potentials than required for NarGH nitrate reduction. The potentials required for Nap nitrate reduction are also likely to require ubiquinol/ubiquinone ratios higher than are needed to activate the H+-pumping oxidases expressed during aerobic growth where Nap levels are maximal. Thus the operational potentials of P. pantotrophus NapAB are consistent with a productive role in redox balancing. A Michaelis constant (KM) of approx. 45 μM was determined for NapAB nitrate reduction at pH 7. This is in line with studies on intact cells where nitrate reduction by Nap was described by a Monod constant (KS) of less than 15 μM. The voltammetric studies also disclosed maximal NapAB activity in a narrow window of potential. This behaviour is resistant to change of pH, nitrate concentration and inhibitor concentration and its possible mechanistic origins are discussed.

scholarly journals High-Intensity Focused Ultrasound Circular Cyclocoagulation in Glaucoma: A Step Forward for Cyclodestruction?

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Rodolfo Mastropasqua ◽  
Vincenzo Fasanella ◽  
Alessandra Mastropasqua ◽  
Marco Ciancaglini ◽  
Luca Agnifili
Keyword(s):  
High Intensity ◽  
Ciliary Body ◽  
Focused Ultrasound ◽  
Current Knowledge ◽  
High Intensity Focused Ultrasound ◽  
High Rate ◽  
Dose Effect ◽  
Computer Assisted ◽  
Refractory Glaucoma ◽  
High Level

The ciliary body ablation is still considered as a last resort treatment to reduce the intraocular pressure (IOP) in uncontrolled glaucoma. Several ablation techniques have been proposed over the years, all presenting a high rate of complications, nonselectivity for the target organ, and unpredictable dose-effect relationship. These drawbacks limited the application of cyclodestructive procedures almost exclusively to refractory glaucoma. High-intensity focused ultrasound (HIFU), proposed in the early 1980s and later abandoned because of the complexity and side effects of the procedure, was recently reconsidered in a new approach to destroy the ciliary body. Ultrasound circular cyclocoagulation (UC3), by using miniaturized transducers embedded in a dedicated circular-shaped device, permits to selectively treat the ciliary body in a one-step, computer-assisted, and non-operator-dependent procedure. UC3 shows a high level of safety along with a predictable and sustained IOP reduction in patients with refractory glaucoma. Because of this, the indication of UC3 was recently extended also to naïve-to-surgery patients, thus reconsidering the role and timing of ciliary body ablation in the surgical management of glaucoma. This article provides a review of the most used cycloablative techniques with particular attention to UC3, summarizing the current knowledge about this procedure and future possible developments.

Consensus document on radiotherapy in patients with implantable pacemakers and cardioverter – defibrilators

2018 ◽  
Vol 2 (47) ◽  
pp. 27-31
Author(s):  
Lidia Chmielewska-Michalak ◽  
Ewelina Konstanty ◽  
Przemysław Mitkowski
Keyword(s):  
Current Knowledge ◽  
Clinical Status ◽  
Electronic Devices ◽  
Heart Rhythm ◽  
Complex Care ◽  
Consensus Document ◽  
Cardiac Implantable Electronic Devices ◽  
Number Of Patients ◽  
High Level ◽  
Emergency Mode

The number of patients with cardiac implantable electronic devices (CIED), who require oncological management including radiotherapy (RT) is still increasing. According to current knowledge the most frequent device dysfunction related to exposition to ionizing radiation is reprogramming to emergency mode (soft reset). There are uncommon cases of complete, irreversible device damage. CIED dysfunction during RT can be observed in approximately 3% of patients. In majority of cases they are asymptomatic, although in literature there are descriptions of deterioration of clinical status due to bradycardia or exacerbation of heart failure. The most important factor of device malfunction is radiotherapy with photons of energy >10 MV or protons despite energy used. So far there were no cases published with inadequate ICD therapies due to the presence of electromagnetic field interference during RT. Because patients with CIED undergoing RT need complex care to achieve high level of safety, experts of Heart Rhythm Society establish document, published in 2017 which summarized current knowledge about this group of patients. The document contains guidelines on peri-radiotherapy care of patients with CIED.

scholarly journals Discovering the Hidden Secondary Metabolome of Myxococcus xanthus: a Study of Intraspecific Diversity

2008 ◽  
Vol 74 (10) ◽  
pp. 3058-3068 ◽  
Author(s):  
Daniel Krug ◽  
Gabriela Zurek ◽  
Ole Revermann ◽  
Michiel Vos ◽  
Gregory J. Velicer ◽  
...  
Keyword(s):  
Secondary Metabolites ◽  
Myxococcus Xanthus ◽  
Single Species ◽  
Intraspecific Diversity ◽  
Metabolic Diversity ◽  
Model Species ◽  
Metabolite Profiles ◽  
High Level ◽  
New Compounds ◽  
Promising Source

ABSTRACT As a monophyletic group, the myxobacteria are known to produce a broad spectrum of secondary metabolites. However, the degree of metabolic diversity that can be found within a single species remains unexplored. The model species Myxococcus xanthus produces several metabolites also present in other myxobacterial species, but only one compound unique to M. xanthus has been found to date. Here, we compare the metabolite profiles of 98 M. xanthus strains that originate from 78 locations worldwide and include 20 centimeter-scale isolates from one location. This screen reveals a strikingly high level of intraspecific diversity in the M. xanthus secondary metabolome. The identification of 37 nonubiquitous candidate compounds greatly exceeds the small number of secondary metabolites previously known to derive from this species. These results suggest that M. xanthus may be a promising source of future natural products and that thorough intraspecific screens of other species could reveal many new compounds of interest.

Characterisation of glyphosate uptake into grass species

2003 ◽  
Vol 54 (9) ◽  
pp. 877 ◽  
Author(s):  
Z. Q. Liu
Keyword(s):  
Leaf Surface ◽  
Current Knowledge ◽  
Grass Species ◽  
Droplet Spreading ◽  
Barnyard Grass ◽  
Spread Area ◽  
Per Se ◽  
High Level ◽  
Content Range ◽  
Determining Factor

The effect of surfactant ethylene oxide (EO) content, droplet spread area, and the active ingredient (a.i.) dose on the leaf surface on glyphosate uptake into 3 grass species (wheat, ryegrass, and barnyard grass) was investigated. It was found that glyphosate uptake into wheat was only moderately correlated (R2 = 0.66) with surfactant EO content (range 5–20 units per molecule). By contrast, a highly negative correlation (R2 = 0.98) was found between the uptake and the spread area of the treatment formulations on the leaf surface. The influence of droplet spreading on glyphosate uptake was further investigated using a super-spreading surfactant, Silwet L-77, and varying a.i. concentrations. It was demonstrated that the determining factor for glyphosate uptake into all 3 grass species was the a.i. dose (in μg/mm2) formed on the leaf surface after droplet spreading. Droplet spread area per se had only an indirect effect on the uptake through diluting the a.i. dose. In the presence of a non-spreading surfactant, Mon 0818, glyphosate uptake depended not only on the a.i. dose but also the surfactant dose on the leaf surface. In the absence of surfactants, high a.i. dose alone was not enough to ensure a high level uptake. The results are discussed in relation to the current knowledge on the interactions between surfactants and herbicide uptake.

scholarly journals Overexpression of the chloroplastic 2-oxoglutarate/malate transporter disturbs carbon and nitrogen homeostasis in rice

2020 ◽  
Author(s):  
Shirin Zamani-Nour ◽  
Hsiang-Chun Lin ◽  
Berkley J Walker ◽  
Tabea Mettler-Altmann ◽  
Roxana Khoshravesh ◽  
...  
Keyword(s):  
C4 Photosynthesis ◽  
Tricarboxylic Acid Cycle ◽  
Carbon Assimilation ◽  
Amino Acid Content ◽  
Glutamate Synthase ◽  
Co2 Assimilation ◽  
Bundle Sheath Cells ◽  
Redox Poise ◽  
High Level ◽  
Malate Transporter

Abstract The chloroplastic 2-oxaloacetate (OAA)/malate transporter (OMT1 or DiT1) takes part in the malate valve that protects chloroplasts from excessive redox poise through export of malate and import of OAA. Together with the glutamate/malate transporter (DCT1 or DiT2), it connects carbon with nitrogen assimilation, by providing 2-oxoglutarate for the GS/GOGAT (glutamine synthetase/glutamate synthase) reaction and exporting glutamate to the cytoplasm. OMT1 further plays a prominent role in C4 photosynthesis: OAA resulting from phosphoenolpyruvate carboxylation is imported into the chloroplast, reduced to malate by plastidic NADP-malate dehydrogenase, and then exported for transport to bundle sheath cells. Both transport steps are catalyzed by OMT1, at the rate of net carbon assimilation. To engineer C4 photosynthesis into C3 crops, OMT1 must be expressed in high amounts on top of core C4 metabolic enzymes. We report here high-level expression of ZmOMT1 from maize in rice (Oryza sativa ssp. indica IR64). Increased activity of the transporter in transgenic rice was confirmed by reconstitution of transporter activity into proteoliposomes. Unexpectedly, overexpression of ZmOMT1 in rice negatively affected growth, CO2 assimilation rate, total free amino acid content, tricarboxylic acid cycle metabolites, as well as sucrose and starch contents. Accumulation of high amounts of aspartate and the impaired growth phenotype of OMT1 rice lines could be suppressed by simultaneous overexpression of ZmDiT2. Implications for engineering C4 rice are discussed.

scholarly journals Constraints on models for the flagellar rotary motor

2000 ◽  
Vol 355 (1396) ◽  
pp. 491-501 ◽  
Author(s):  
Howard C. Berg
Keyword(s):  
Hydrogen Isotope ◽  
Room Temperature ◽  
Cytoplasmic Membrane ◽  
Sodium Ion ◽  
Protonmotive Force ◽  
Revolution Speed ◽  
High Speeds ◽  
Rotary Motor ◽  
Inside Out ◽  
Do So

Most bacteria that swim are propelled by flagellar filaments, each driven at its base by a rotary motor embedded in the cell wall and cytoplasmic membrane. A motor is about 45 nm in diameter and made up of about 20 different kinds of parts. It is assembled from the inside out. It is powered by a proton (or in some species, a sodium–ion) flux. It steps at least 400 times per revolution. At low speeds and high torques, about 1000 protons are required per revolution, speed is proportional to protonmotive force, and torque varies little with temperature or hydrogen isotope. At high speeds and low torques, torque increases with temperature and is sensitive to hydrogen isotope. At room temperature, torque varies remarkably little with speed from about –100 Hz (the present limit of measurement) to about 200 Hz, and then it declines rapidly, reaching zero at about 300 Hz. These are facts that motor models should explain. None of the existing models for the flagellar rotary motor completely do so.

Iron Overload, Oxidative Damage and Ineffective Erythropoiesis in Myelodysplastic Syndromes

2010 ◽  
Vol 00 (04) ◽  
pp. 34 ◽  
Author(s):  
Rosangela Invernizzi ◽  
Keyword(s):  
Oxidative Damage ◽  
Iron Overload ◽  
Myelodysplastic Syndromes ◽  
Iron Homeostasis ◽  
Current Knowledge ◽  
Early Stage ◽  
Refractory Anaemia ◽  
Ineffective Erythropoiesis ◽  
Ring Sideroblasts ◽  
High Level

A high level of apoptosis may be responsible for the ineffective haematopoiesis in myelodysplastic syndromes (MDS). Recently, it has been demonstrated that the erythroid apoptosis of low-risk MDS is initiated at a very early stage in stem cells and is associated with mitochondrial dysfunction. However, the underlying pathogenetic mechanisms causing malfunctioning of mitochondria and initiation of the intrinsic apoptotic cascade are not completely clear. Recent studies suggest a close relationship between impaired iron metabolism and pathogenesis of myelodysplasia. In fact, iron overload, which is apparent in refractory anaemia with and without ring sideroblasts, may lead to the generation of intracellular free radicals, thereby causing oxidative damage and inducing apoptosis in haematopoietic progenitors. This review summarises current knowledge supporting the role of iron-related oxidative damage in the pathogenesis of MDS. The relationship between mitochondrial iron homeostasis impairment and ineffective erythropoiesis in refractory anaemia with ring sideroblasts as well as the various functions of the cytosolic and mitochondrial ferritins are also discussed.

scholarly journals The mechanism of proton translocation driven by the respiratory nitrate reductase complex of Escherichia coli

1980 ◽  
Vol 190 (1) ◽  
pp. 79-94 ◽  
Author(s):  
Robert W. Jones ◽  
Alan Lamont ◽  
Peter B. Garland
Keyword(s):  
Escherichia Coli ◽  
Nitrate Reductase ◽  
Mutant Strain ◽  
Cytoplasmic Membrane ◽  
Reductase Activity ◽  
Proton Translocation ◽  
Deficient Mutant ◽  
Benzyl Viologen ◽  
Low Concentrations ◽  
Nitrite Reductase Activity

Low concentrations (1–50μm) of ubiquinol1 were rapidly oxidized by spheroplasts of Escherichia coli derepressed for synthesis of nitrate reductase using either nitrate or oxygen as electron acceptor. Oxidation of ubiquinol1 drove an outward translocation of protons with a corrected →H+/2e− stoichiometry [Scholes & Mitchell (1970) J. Bioenerg.1, 309–323] of 1.49 when nitrate was the acceptor and 2.28 when oxygen was the acceptor. Proton translocation driven by the oxidation of added ubiquinol1 was also observed in spheroplasts from a double quinone-deficient mutant strain AN384 (ubiA−menA−), whereas a haem-deficient mutant, strain A1004a, did not oxidize ubiquinol1. Proton translocation was not observed if either the protonophore carbonyl cyanide m-chlorophenylhydrazone or the respiratory inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide was present. When spheroplasts oxidized Diquat radical (DQ+) to the oxidized species (DQ++) with nitrate as acceptor, nitrate was reduced to nitrite according to the reaction: [Formula: see text] and nitrite was further reduced in the reaction: [Formula: see text] Nitrite reductase activity (2) was inhibited by CO, leaving nitrate reductase activity (1) unaffected. Benzyl Viologen radical (BV+) is able to cross the cytoplasmic membrane and is oxidized directly by nitrate reductase to the divalent cation, BV++. In the presence of CO, this reaction consumes two protons: [Formula: see text] The consumption of these protons could not be detected by a pH electrode in the extra-cellular bulk phase of a suspension of spheroplasts unless the cytoplasmic membrane was made permeable to protons by the addition of nigericin or tetrachlorosalicylanilide. It is concluded that the protons of eqn. (3) are consumed at the cytoplasmic aspect of the cytoplasmic membrane. Diquat radical, reduced N-methylphenazonium methosulphate and its sulphonated analogue N-methylphenazonium-3-sulphonate (PMSH) and ubiquinol1 are all oxidized by nitrate reductase via a haem-dependent, endogenous quinone-independent, 2-n-heptyl-4-hydroxyquinoline N-oxide-sensitive pathway. Approximate→H+/2e− stoichiometries were zero with Diquat radical, an electron donor, 1.0 with reduced N-methylphenazonium methosulphate or its sulphonated analogue, both hydride donors, and 2.0 with ubiquinol1 (QH2), a hydrogen donor. It is concluded that the protons appearing in the medium are derived from the reductant and the observed→H+/2e− stoichiometries are accounted for by the following reactions occurring at the periplasmic aspect of the cytoplasmic membrane.: [Formula: see text]

Structural diversity in echinocandin biosynthesis: the impact of oxidation steps and approaches toward an evolutionary explanation

2017 ◽  
Vol 72 (1-2) ◽  
pp. 1-20 ◽  
Author(s):  
Wolfgang Hüttel
Keyword(s):  
Secondary Metabolism ◽  
Current Knowledge ◽  
Structural Diversity ◽  
Special Focus ◽  
Oxidation Reactions ◽  
Metabolic Diversity ◽  
Comprehensive Overview ◽  
Single Organism ◽  
The Impact ◽  
Best Fit

AbstractEchinocandins are an important group of cyclic non-ribosomal peptides with strong antifungal activity produced by filamentous fungi from Aspergillaceae and Leotiomycetes. Their structure is characterized by numerous hydroxylated non-proteinogenic amino acids. Biosynthetic clusters discovered in the last years contain up to six oxygenases, all of which are involved in amino acid modifications. Especially, variations in the oxidation pattern induced by these enzymes account for a remarkable structural diversity among the echinocandins. This review provides an overview of the current knowledge of echinocandin biosynthesis with a special focus on diversity-inducing oxidation steps. The emergence of metabolic diversity is further discussed on the basis of a comprehensive overview of the structurally characterized echinocandins, their producer strains and biosynthetic clusters. For the pneumocandins, echinocandins produced byGlarea lozoyensis, the formation of metabolic diversity in a single organism is analyzed. It is compared to two common models for the evolution of secondary metabolism: the ‘target-based’ approach and the ‘diversity-based’ model. Whereas the early phase of pneumocandin biosynthesis supports the target-based model, the diversity-inducing late steps and most oxidation reactions best fit the diversity-based approach. Moreover, two types of diversity-inducing steps can be distinguished. Although incomplete hydroxylation is a common phenomenon in echinocandin production and secondary metabolite biosynthesis in general, the incorporation of diverse hydroxyprolines at position 6 is apparently a unique feature of pneumocandin biosynthesis, which stands in stark contrast to the strict selectivity found in echinocandin biosynthesis by Aspergillaceae. The example of echinocandin biosynthesis shows that the existing models for the evolution of secondary metabolism can be well applied to parts of the pathway; however, thus far, there is no comprehensive theory that could explain the entire biosynthesis.

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