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See detailElectron partitioning between the two branching quinol-oxidizing pathways in Acanthamoeba castellanii mitochondria during steady-state state 3 respiration.
Jarmuszkiewicz, W.; Sluse-Goffart, C.; Hryniewiecka, L. et al

in Journal of Biological Chemistry (1997), 273(17), 10174-10180

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non ... [more ▼]

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non-phosphorylating property of alternative oxidase, was used to determine contributions of both pathways in overall state 3 respiration in the presence of GMP (an activator of the alternative oxidase in amoeba) and succinate as oxidizable substrate. This method involves pair measurements of ADP/O ratios plus and minus benzohydroxamate (an inhibitor of the alternative oxidase). The requirements of the method are listed and verified. When overall state 3 respiration was decreased by increasing concentrations of n-butyl malonate (a non-penetrating inhibitor of succinate uptake), the quinone reduction level declined. At the same time, the alternative pathway contribution decreased sharply and became negligible when quinone redox state was lower than 50%, whereas the cytochrome pathway contribution first increased and then passed through a maximum at a quinone redox state of 58% and sharply decreased at a lower level of quinone reduction. This study is the first attempt to examine the steady-state kinetics of the two quinol-oxidizing pathways when both are active and to describe electron partitioning between them when the steady-state rate of the quinone-reducing pathway is varied. [less ▲]

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See detailElectron photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores
Gabelica, Valérie ULg; Rosu, Frédéric ULg; De Pauw, Edwin ULg et al

in Journal of the American Society for Mass Spectrometry (2007), 18(11), 1990-2000

Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation. in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound ... [more ▼]

Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation. in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound minor groove binders (activated in the near UV), noncovalently bound intercalators (activated with visible light), and covalently linked fluorophores and quenchers (activated at their maximum absorption wavelength). We found that the activation of only chromophores having long fluorescence lifetimes did result in efficient electron photodetachment from the DNA complexes. In the case of ethidium-dsDNA complex excited at 500 nm, photodetachment is a multiphoton process. The MS3 fragmentation of radicals produced by photodetachment at lambda = 260 nm (DNA excitation) and by photodetachment at lambda > 300 nm (chromophore excitation) were compared. The radicals keep no memory of the way they were produced. A weakly bound noncovalent ligand (m-amsacrine) allowed probing experimentally that a fraction of the electronic internal energy was converted into vibrational internal energy. This fragmentation channel was used to demonstrate that excitation of the quencher DABSYL resulted in internal conversion, unlike the fluorophore 6-FAM. Altogether, photodetachment of the DNA complexes upon chromophore excitation can be interpreted by the following mechanism: (1) ligands with sufficiently long excited-state lifetime undergo resonant two-photon excitation to reach the level of the DNA excited states, then (2) the excited-state must be coupled to the DNA excited states for photodetachment to occur. Our experiments also pave the way towards photodissociation probes of biomolecule conformation in the gas-phase by Forster resonance energy transfer (FRET). [less ▲]

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See detailElectron photodetachment dissociation of DNA polyanions in a quadrupole ion trap mass spectrometer
Gabelica, Valérie ULg; Tabarin, Thibault; Antoine, Rodolphe et al

in Analytical Chemistry (2006), 78(18), 6564-6572

We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer ... [more ▼]

We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer single strands and 12-base pair double strands. In all cases, laser irradiation causes electron detachment from the multiply charged DNA anions. Electron photodetachment efficiency directly depends on the number of guanines in the strand, and maximum efficiency is observed between 260 and 275 nm. Subsequent collision-induced dissociation (CID) of the radical anions produced by electron photodetachment results in extensive fragmentation. In addition to neutral losses, a large number of fragments from the w, d, a*, and z* ion series are obtained, contrasting with the w and (a-base) ion series observed in regular CID. The major advantage of this technique, coined electron photodetachment dissociation (EPD) is the absence of internal fragments, combined with good sequence coverage. EPD is therefore a highly promising approach for de novo sequencing of oligonucleotides. EPD of nucleic acids is also expected to give specific radical-induced strand cleavages, with conservation of other fragile bonds, including noncovalent bonds. In effect, preliminary results on a DNA hairpin and on double strands suggest that EPD could also be used to probe intra- and intermolecular interactions in nucleic acids. [less ▲]

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See detailElectron Photodetachment of DNA Polyanions: Photoelectron Spectroscopy and UV Action Spectroscopy
Gabelica, Valérie ULg; Rosu, Frédéric ULg; De Pauw, Edwin ULg et al

Conference (2008, April 15)

DNA polyanions trapped in a mass spectrometer undergo electron detachment following irradiation with UV light [1-3]. Electron photodetachment is a 1-photon process, and its efficiency depends on: - The ... [more ▼]

DNA polyanions trapped in a mass spectrometer undergo electron detachment following irradiation with UV light [1-3]. Electron photodetachment is a 1-photon process, and its efficiency depends on: - The nature of the DNA bases: guanine-containing strands are the most prone to electron photodetachment, followed by adenine, cytosine, and finally thymine. - The excitation wavelength: electron detachment is maximum around 260 nm, corresponding to base excitation. - The charge of the polyanion: higher charge state ions undergo more efficient electron detachment because of the Coulombic repulsion. Here we will discuss the electron photodetachment mechanism in the light of the most recent experimental results. Because the base-dependence of electron photodetachment efficiency is correlated with the base ionization potential and is maximum at wavelengths corresponding to the base absorption, we initially proposed that electron photodetachment might occur directly from the base, and that the photodetachment yield was correlated with the electron binding energy to the base [2]. Photoelectron spectroscopy experiments were performed on DNA multiply charged anions with varying base composition to probe how the electron binding energies changes with the base composition. Finally, the electron detachment channel was used to perform UV spectroscopy experiments on large DNA polyanions trapped in the gas phase. Gas-phase UV spectra of DNA duplexes and G-quadruplexes containing up to 24 bases (> 7000 Da) will be presented. [1] V. Gabelica, T. Tabarin, R. Antoine, F. Rosu, I. Compagnon, M. Broyer, E. De Pauw, and P. Dugourd, Anal. Chem. 78, 6564 (2006). [2] V. Gabelica, F. Rosu, T. Tabarin, C. Kinet, R. Antoine, M. Broyer, E. De Pauw, and P. Dugourd, J. Am. Chem. Soc. 129, 4706 (2007). [3] V. Gabelica, F. Rosu, E. De Pauw, R. Antoine, T. Tabarin, M. Broyer, and P. Dugourd, J. Am. Soc. Mass Spectrom. 18, 1990 (2007). [less ▲]

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See detailAn Electron Spin Resonance (Esr) Study on the Mechanism of Ascorbyl Radical Production by Metal-Binding Proteins
Mouithys-Mickalad, Ange ULg; Deby, Carol; Dupont, Ginette ULg et al

in Biometals (1998), 11(2), 81-8

The mechanism of ascorbate oxidation by metal-binding proteins (ceruloplasmin, albumin and transferrin) was investigated in vitro and in isolated plasma by the measurement of the ascorbyl free radicals ... [more ▼]

The mechanism of ascorbate oxidation by metal-binding proteins (ceruloplasmin, albumin and transferrin) was investigated in vitro and in isolated plasma by the measurement of the ascorbyl free radicals (AFR) by electron spin resonance (ESR). In plasma of 13 healthy volunteers, a spontaneous and variable production of AFR was detected, which was increased by a 10(-4) M ascorbate overloading; however, this increase was not correlated to the intensity of the spontaneous AFR signal. The addition of Cu2+ and ceruloplasmin to plasma increased the ESR signal, while the addition of transferrin decreased the signal intensity in a dose-dependent manner. In vitro, we demonstrated that ascorbate was oxidized by human serum albumin and by ceruloplasmin, and that this oxidase-like activity was lost by trypsin or heat treatment of these proteins. These two proteins positively interacted in the oxidation of ascorbate, since addition of crude albumin to a solution of ascorbate and ceruloplasmin increased the intensity of ESR signal in a dose-dependent manner. The treatment of albumin by a metal chelator (DDTC) abolished these positive interactions. The respective roles of copper and iron in ascorbate oxidation were studied and showed a dose-dependent effect of these ions on ascorbate oxidation. The role of iron was confirmed by the inhibiting effect of metal-free transferrin on iron-dependent ascorbate oxidation. Concerted actions between iron carrying albumin and copper carrying ceruloplasmin appear responsible for the production of AFR in vitro and in vivo. [less ▲]

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See detailElectron Spin Resonance Evidence of the Generation of Superoxide Anion, Hydroxyl Radical and Singlet Oxygen During the Photohemolysis of Human Erythrocytes with Bacteriochlorin A
Hoebeke, Maryse ULg; Schuitmaker, H. J.; Jannink, L. E. et al

in Photochemistry & Photobiology (1997), 66(4), 502-8

Photodynamic therapy with bacteriochlorin a (BCA) as sensitizer induces damage to red blood cells in vivo. To assess the extent of the contributuion of reactive oxygen species (ROS) and to determine a ... [more ▼]

Photodynamic therapy with bacteriochlorin a (BCA) as sensitizer induces damage to red blood cells in vivo. To assess the extent of the contributuion of reactive oxygen species (ROS) and to determine a possible reaction mechanism, competition experiments with assorted ROS quenching or/and enhancing agents were performed in human erythrocytes as model system and in phosphate buffer. In the erythrocyte experiments, a 2% suspension was incubated with BCA for 1 h, washed with phosphate-buffered saline, resuspended and subsequently illuminated with a diode laser using a fluence rate of 2.65 mW/cm2. Potassium leakage and hemolysis were light and BCA dose dependent. Adding tryptophan (3.3 mM), azide (1 mM) or histidine (10 mM) to the erythrocyte suspension before illumination delayed the onset of K-leakage and hemolysis suggesting a type II mechanism. The D2O did not affect K-leakage nor photohemolysis. Adding mannitol (13.3 mM) or glycerol (300 nM) also caused a delay in the onset of K-leakage and hemolysis, suggesting the involvement of radicals. In phosphate buffer experiments, it was shown using electron spin resonance (ESR) associated with spin-trapping techniques that BCA is able to generate O2-. and OH. radicals without production of aqueous electron. Visible or UV irradiation of the dye in the presence of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) gave an ESR spectrum characteristic of the DMPO-hydroxyl radical spin adduct DMPO-OH. Addition of ethanol or sodium formate produced supplementary hyperfine splittings due to the respective CH3CHOH. and CO2-. radical adducts, indicating the presence of free OH.. Production of DMPO-OH was partly inhibited by superoxide dismutase (SOD), catalase and desferrioxamine, suggesting that the iron-catalyzed decomposition of H2O2 was partly involved in the formation of one part of the observed OH.. The complementary inhibition of DMPO-OH production by azide and 9,10-anthracenedipropionic acid (ADPA) was consistent with 1O2 production by BCA followed by reaction of 1O2 with DMPO and decay of the intermediate complex to form DMPO-OH and free OH.. All our results seem to indicate that BCA is a 50%/50% type 1/type 2 sensitizer in buffered aqueous solutions and confirmed that the dye-induced hemolysis of erythrocytes was cell caused by a mixed type 1/type 2 mechanism. [less ▲]

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See detailElectron spin resonance study of basteriochlorin a incorporation into membranes models
Hoebeke, Maryse ULg; Damoiseau, X.; Schuitmaker, H. et al

Conference (1999)

Detailed reference viewed: 2 (1 ULg)
See detailElectron spin resonance study of basteriochlorin a incorporation into membranes models
Hoebeke, Maryse ULg; Damoiseau, X.; Schuitmaker, H. et al

Conference (1999)

Detailed reference viewed: 2 (1 ULg)
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See detailElectron tomography of metaphase nucleolar organizer regions: evidence for a twisted-loop organization.
Heliot, L.; Kaplan, H.; Lucas, L. et al

in Molecular Biology of the Cell (1997), 8(11), 2199-216

Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins ... [more ▼]

Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins such as upstream binding factor and RNA polymerase I, which are argyrophilic NOR proteins. Immunocytochemical and cytochemical labelings of these proteins were used to reveal r-chromatin in situ and to investigate its spatial organization within NORs by confocal microscopy and by electron tomography. For each labeling, confocal microscopy revealed small and large double-spotted NORs and crescent-shaped NORs. Their internal three-dimensional (3D) organization was studied by using electron tomography on specifically silver-stained NORs. The 3D reconstructions allow us to conclude that the argyrophilic NOR proteins are grouped as a fiber of 60-80 nm in diameter that constitutes either one part of a turn or two or three turns of a helix within small and large double-spotted NORs, respectively. Within crescent-shaped NORs, virtual slices reveal that the fiber constitutes several longitudinally twisted loops, grouped as two helical 250- to 300-nm coils, each centered on a nonargyrophilic axis of condensed chromatin. We propose a model of the 3D organization of r-chromatin within elongated NORs, in which loops are twisted and bent to constitute one basic chromatid coil. [less ▲]

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See detailElectron-atmosphere interaction in the aurora of giant planets
Gérard, Jean-Claude ULg

Conference (2010, October 18)

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of ... [more ▼]

All methods converge to indicate that the efficiency of the H2 (B,C states) emission is close to 10 kR/mW m-2 of electron precipitation. The UV aurora is a direct instantaneous map of the distribution of the electron precipitation. By contrast, the IR H3+ aurora is indirectly produced and its intensity depends on the amount of H3+ ions and the local temperature. It has the advantage to be observable from the ground The «UV color ratio » method is a powerful tool to probe the electron mean energy IF the distribution of HCs (mostly methane) is known EUV spectroscopy is very useful to determine the depth of the electron energy deposition, but so far, without spatial resolution [less ▲]

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See detailElectron-deficient 1- and 2-aza-1,3-dienes: a comprehensive survey of their synthesis and reactivity
Monbaliu, Jean-Christophe ULg; Masschelein, Kurt; Stevens, Christian

in Chemical Society Reviews (2011), 40

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See detailElectron-microscopic tomography of silver-stained interphase and metaphase nucleolar organizer regions
Cheutin, T; O'Donohue, M-F; Kaplan, H et al

Poster (1999)

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See detailElectroneuromyographie
WANG, François-Charles ULg; FOIDART, Marguerite ULg; Chantraine, Alex

in Chantraine, Alex (Ed.) Rééducation neurologique guide pratique de rééducation des affections neurologiques (2013)

Detailed reference viewed: 33 (2 ULg)