Articles

Ligand dynamics in an electron-transfer protein: picosecond geminate recombination of carbon monoxide to heme in mutant forms of cytochrome c
- Silkstone Gary
- Jasaitis Audrius
- Wilson M. T.
- Vos Marten H.
Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology , 2007, 282, pp.1638-1649 . Substitution of the heme coordination residue Met-80 of the electron transport protein yeast iso-1-cytochrome c allows external ligands like CO to bind and thus increase the effective redox potential. This mutation, in principle, turns the protein into a quasi-native photoactivable electron donor. We have studied the kinetic and spectral characteristics of geminate recombination of heme and CO in a series of single M80X (X = Ala, Ser, Asp, Arg) mutants, using femtosecond transient absorption spectroscopy. In these proteins, all geminate recombination occurs on the picosecond and early nanosecond time scale, in a multiphasic manner, in which heme relaxation takes place on the same time scale. The extent of geminate recombination varies from >99% (Ala, Ser) to ∼70% (Arg), the latter value being in principle low enough for electron injection studies. The rates and extent of the CO geminate recombination phases are much higher than in functional ligand-binding proteins like myoglobin, presumably reflecting the rigid and hydrophobic properties of the heme environment, which are optimized for electron transfer. Thus, the dynamics of CO recombination in cytochrome c are a tool for studying the heme pocket, in a similar way as NO in myoglobin. We discuss the differences in the CO kinetics between the mutants in terms of the properties of the heme environment and strategies to enhance the CO escape yield. Experiments on double mutants in which Phe-82 is replaced by Asp or Gly as well as the M80D substitution indicate that such steric changes substantially increase the motional freedom-dissociated CO. (10.1074/jbc.M605760200)
DOI : 10.1074/jbc.M605760200
Distal Val346Ile mutation in inducible NO synthase promotes substrate-dependent NO confinement
- Beaumont Edward
- Lambry Jean-Christophe
- Wang Z.-Q.
- Stuehr D.J.
- Martin Jean-Louis
- Slama-Schwok Anny
Biochemistry, American Chemical Society , 2007, 46 (47), pp.13533 . The function of inducible NO synthase (WT iNOS) depends on the release of NO from the ferric heme before the enzyme is reduced. Key parameters controlling ligand dynamics include the distal and proximal heme pocket amino acids, as well as the inner solvent molecules. In this work, we tested how a point mutation in the distal heme side of WT iNOS affected the geminate rebinding of NO by ultrafast kinetics and molecular dynamics simulations. The mutation sequestered much of the photodissociated NO close to the heme compared to WT iNOS, with a main picosecond phase accounting for 78% of the rebinding to the arginine-bound Val346Ile protein. Consequently, the probability of NO release from Val346Ile decreased as compared to that from WT iNOS, provided the substrate binding site is filled. These data are rationalized by a steric effect of the Ile methyl group inducing events mediated by the substrate, transmitted via the propionates to the NO and the protein. This model is consistent with the role of the H-bonding network involving the heme, the substrate, and the BH4 cofactor in controlling NO release, with a key role of the heme propionates [Gautier et al. (2006) Nitric Oxide 15, 312]. These data support the effect of Val346Ile mutation in decreasing NO release and slowing down NO synthesis compared to WT iNOS determined by single turnover catalysis [Wang et al. (2004) J. Biol. Chem. 279, 19018]. Cop. 2007 American Chemical Society. (10.1021/bi701567h)
DOI : 10.1021/bi701567h
1-kHz table-top ultrashort hard x-ray source for time-resolved x-ray protein
- Bonvalet Adeline
- Darmon Adeline
- Lambry Jean-Christophe
- Martin Jean-Louis
- Audebert Patrick
Optics Letters, Optical Society of America - OSA Publishing , 2006, 31 (18), pp.2753 . We describe a compact, reliable, and high-average-power femtosecond x-ray source and its first application to diffraction on protein crystal. The setup relies on a homemade Ti: sapphire system delivering 12 mJ at a 1 kHz repetition rate, associated with a small vacuum chamber especially designed for laser-plasma interaction and x-ray applications. This device allows the generation of 5×109 photons/s/sr at 8 keV and optimized x-ray irradiation of the studied sample, which can be placed close to the source. We present the diffraction pattern of a protein crystal in a divergent beam geometry, which is a first step to a subpicosecond x-ray diffraction experiment. (10.1364/OL.31.002753)
DOI : 10.1364/OL.31.002753
Catalytic mechanism and structure of viral flavin-dependent thymidylate synthase ThyX.
- Graziani Sébastien
- Bernauer Julie
- Skouloubris Stéphane
- Graille Marc
- Zhou Cong-Zhao
- Marchand Christophe
- Decottignies Paulette
- van Tilbeurgh Herman
- Myllykallio Hannu
- Liebl Ursula
Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology , 2006, 281 (33), pp.24048-57 . By using biochemical and structural analyses, we have investigated the catalytic mechanism of the recently discovered flavin-dependent thymidylate synthase ThyX from Paramecium bursaria chlorella virus-1 (PBCV-1). Site-directed mutagenesis experiments have identified several residues implicated in either NADPH oxidation or deprotonation activity of PBCV-1 ThyX. Chemical modification by diethyl pyrocarbonate and mass spectroscopic analyses identified a histidine residue (His53) crucial for NADPH oxidation and located in the vicinity of the redox active N-5 atom of the FAD ring system. Moreover, we observed that the conformation of active site key residues of PBCV-1 ThyX differs from earlier reported ThyX structures, suggesting structural changes during catalysis. Steady-state kinetic analyses support a reaction mechanism where ThyX catalysis proceeds via formation of distinct ternary complexes without formation of a methyl enzyme intermediate. (10.1074/jbc.M600745200)
DOI : 10.1074/jbc.M600745200
Ultrafast heme dynamics in ferrous versus ferric cytochrome c studied by time-resolved resonance Raman and transient absorption spectroscopy.
- Négrerie Michel
- Cianetti Simona
- Vos Marten H.
- Martin Jean-Louis
- Kruglik Sergei G.
Journal of Physical Chemistry B, American Chemical Society , 2006, 110 (25), pp.12766-12781 . Cytochrome c (Cyt c) is a heme protein involved in electron transfer and also in apoptosis. Its heme iron is bisaxially ligated to histidine and methionine side chains and both ferric and ferrous redox states are physiologically relevant, as well as a ligand exchange between internal residue and external diatomic molecule. The photodissociation of internal axial ligand was observed for several ferrous heme proteins including Cyt c, but no time-resolved studies have been reported on ferric Cyt c. To investigate how the oxidation state of the heme influences the primary photoprocesses, we performed a comprehensive comparative study on horse heart Cyt c by subpicosecond time-resolved resonance Raman and femtosecond transient absorption spectroscopy. We found that in ferric Cyt c, in contrast to ferrous Cyt c, the photodissociation of an internal ligand does not take place, and relaxation dynamics is dominated by vibrational cooling in the ground electronic state of the heme. The intermolecular vibrational energy transfer was found to proceed in a single phase with a temperature decay of 7 ps in both ferric and ferrous Cyt c. For ferrous Cyt c, the instantaneous photodissociation of the methionine side chain from the heme iron is the dominant event, and its rebinding proceeds in two phases, with time constants of 5 and 16 ps. A mechanism of this process is discussed, and the difference in photoinduced coordination behavior between ferric and ferrous Cyt c is explained by an involvement of the excited electronic state coupled with conformational relaxation of the heme. (10.1021/jp0559377)
DOI : 10.1021/jp0559377
Ultrashort laser pulses and ultrashort electron bunches generated in relativistic laser-plasma interaction
- Faure Jérôme
- Glinec Y.
- Gallot Guilhem
- Malka Victor
Physics of Plasmas, American Institute of Physics , 2006, 13 (5), pp.056706 . An experimental study of the interaction of ultrashort laser pulses with underdense plasmas in the relativistic regime is presented. A parameter regime of particular interest was found: the so-called bubble regime. In this regime, the laser pulse is focused to relativistic intensities and its pulse duration is comparable to or shorter than the plasma period. A wealth of physical phenomena occurs for such physical parameters. These phenomena have multiple signatures which have been investigated experimentally: (i) the generation of a high quality electron beam (high energy, very collimated, quasimonoenergetic energy distribution); (ii) the laser pulse temporal shortening in nonlinear plasma waves. In addition, experimental results suggest that the electron beam produced in this way has temporal structures shorter than 50 fs. (10.1063/1.2180727)
DOI : 10.1063/1.2180727
Fourier-transform coherent anti-Stokes Raman scattering microscopy.
- Ogilvie Jennifer P.
- Beaurepaire Emmanuel
- Alexandrou Antigoni
- Joffre Manuel
Optics Letters, Optical Society of America - OSA Publishing , 2006, 31 (4), pp.480-2 . We report a novel Fourier-transform-based implementation of coherent anti-Stokes Raman scattering (CARS) microscopy. The method employs a single femtosecond laser source and a Michelson interferometer to create two pulse replicas that are fed into a scanning multiphoton microscope. By varying the time delay between the pulses, we time-resolve the CARS signal, permitting easy removal of the nonresonant background while providing high resolution, spectrally resolved images of CARS modes over the laser bandwidth (approximately 1500 cm(-1)). We demonstrate the method by imaging polystyrene beads in solvent. (10.1364/OL.31.000480)
DOI : 10.1364/OL.31.000480
Insight into Framework Destruction in Ultramarine Pigments
- del Federico Eleonora
- Shöfberger Wolfgang
- Schelvis Johannes
- Kapetanaki Sofia
- Tyne Lindsey
- Jerschow Alexej
Inorganic Chemistry, American Chemical Society , 2006, 45 (3), pp.1270-1276 . (10.1021/ic050903z)
DOI : 10.1021/ic050903z
Use of coherent control for selective two-photon fluorescence microscopy in live organisms.
- Ogilvie Jennifer P.
- Débarre Delphine
- Solinas Xavier
- Martin Jean-Louis
- Beaurepaire Emmanuel
- Joffre Manuel
Optics Express, Optical Society of America - OSA Publishing , 2006, 14 (2), pp.759-766 . We demonstrate selective fluorescence We demonstrate selective fluorescence excitation of specific molecular species in live organisms by using coherent control of two-photon excitation. We have acquired quasi-simultaneous images in live fluorescently-labeled Drosophila embryos by rapid switching between appropriate pulse shapes. Linear combinations of these images demonstrate that a high degree of fluorophore selectivity is attainable through phase-shaping. Broadband phase-shaped excitation opens up new possibilities for single-laser, multiplex, in-vivo fluorescence microscopy. © 2006 Optical Society of America (10.1364/OPEX.14.000759)
DOI : 10.1364/OPEX.14.000759
Emission properties and applications of nanostructured luminescent oxide nanoparticles
- Giaume D.
- Buissette V.
- Lahlil K.
- Gacoin T.
- Boilot J.-P.
- Casanova Didier
- Beaurepaire Emmanuel
- Sauviat Martin-Pierre
- Alexandrou Antigoni
Progress in Solid State Chemistry, Elsevier , 2006, 33 (2-4), pp.99 . Rare earth doped oxide materials are well known for their numerous applications in light emitting devices. An interesting issue is to study the emission properties of nanoparticles, with the aim to understand the influence of small size and surface effects on the emission processes. These particles could furthermore be used in new applications such as the elaboration of transparent emitting devices or new biological labels. The work presented here concerns highly luminescent rare earth doped yttrium vanadates (YVO4:Eu) and lanthanum phosphate LaPO4:Ce,Tb*xH2O nanoparticles. Simple aqueous colloidal syntheses are used for the elaboration of concentrated colloids based on the progressive decomposition of polymeric precursors at moderate temperature (60-90 °C). Both types of particles exhibit strong emission (quantum yields of 25% and 45% for vanadates and phosphates, respectively), but significantly lower than that for the equivalent bulk materials. The alteration of the emission processes is discussed in terms of surface quenching effects. Improvements are obtained through the elaboration of core/shell nanostructures. Surface derivatization has been achieved through the controlled growth of an organically modified silica shell using a functionalized silane precursor. Two examples are given concerning the applications of those particles. The first one is the elaboration of transparent and highly luminescent thin films, obtained by the dispersion of the functionalized particles in a sol-gel silica matrix. The other one is the use of guanidine functionalized particles as biological labels for the single particle detection of sodium channels in cardiac cells. (10.1016/j.progsolidstchem.2005.11.041)
DOI : 10.1016/j.progsolidstchem.2005.11.041
Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity
- Masson Jean-Baptiste
- Sauviat Martin-Pierre
- Gallot Guilhem
Applied Physics Letters, American Institute of Physics , 2006, 89 (15), pp.153904 . The authors demonstrate the direct, noninvasive and time resolved imaging of functional frog auricular fibers by ionic contrast terahertz (ICT) near field microscopy. This technique provides quantitative, time-dependent measurement of ionic flow during auricular muscle electrical activity, and opens the way of direct noninvasive imaging of cardiac activity under stimulation. ICT microscopy technique was associated with full three-dimensional simulation enabling to measure precisely the fiber sizes. This technique coupled to waveguide technology should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes. Cop. 2006 American Institute of Physics. (10.1063/1.2360931)
DOI : 10.1063/1.2360931
Dynamics of NO rebinding to the heme domain of NO synthase-like proteins from bacterial pathogens
- Gautier Clément
- Mikula Ivan
- Nioche P.
- Martasek P.
- Raman C.
- Slama-Schwok Anny
Nitric Oxide , 2006, à paraître .
Microscopies multiharmoniques pour l'imagerie structurale de tissus intacts [Second- and third-harmonic generation microscopies for the structural imaging of intact tissues]
- Débarre Delphine
- Pena Ana-Maria
- Supatto Willy
- Boulesteix Thierry
- Strupler Mathias
- Martin Jean-Louis
- Sauviat Martin-Pierre
- Schanne-Klein Marie-Claire
- Beaurepaire Emmanuel
Médecine/Sciences, EDP Sciences , 2006, 22 (10), pp.845 . Depuis son introduction en 1990, la microscopie de fluorescence excitée à deux photons (Fluo-2P) s'est peu à peu imposée comme une méthode incontournable d'imagerie de tissus intacts à l'échelle sub-cellulaire. En effet, la caractéristique la plus remarquable de la microscopie multiphotonique est de maintenir une résolution tridimensionnelle micrométrique lors de l'observation en profondeur d'un milieu optiquement diffusant. Combinée aux technologies de protéines-fusion (type GFP), cette approche est aujourd'hui utilisée dans de nombreux domaines, notamment en neurophysiologie. Un autre attrait de ce type d'imagerie réside dans l'utilisation possible d'autres phénomènes optiques non linéaires (c'est-à-dire impliquant l'interaction simultanée de plusieurs photons avec une molécule observée) comme source de contraste. Ainsi, les microscopies par génération de second harmonique (GSH) et par génération de troisième harmonique (GTH) permettent également d'observer des milieux complexes et fournissent des informations complémentaires par rapport à l'imagerie de fluorescence. Certaines structures cellulaires ou tissulaires fournissent, en effet, ce type de réponse optique sans nécessiter de marquage exogène. La microscopie GSH permet, par exemple, de détecter le collagène fibrillaire et la microscopie GTH permet d'observer sans marquage le développement embryonnaire de petits organismes. One principal advantage of multiphoton excitation microscopy is that it preserves its three-dimensional micrometer resolution when imaging inside light-scattering samples. For that reason two-photon-excited fluorescence microscopy has become an invaluable tool for cellular imaging in intact tissue, with applications in many fields of physiology. This success has driven increasing interest in other forms of nonlinear microscopy that can provide additional information on cells and tissues, such as second- (SHG) and third- (THG) harmonic generation microscopies. In recent years, significant progress has been made in understanding the contrast mechanisms of these recent methodologies, and high-resolution imaging based on intrinsic sources of signal has been demonstrated in cells and tissues. Harmonic generation exhibits structural rather than chemical specificity and can be obtained from a variety of non-fluorescent samples. SHG is observed specifically in dense, non-centrosymmetric arrangements of polarizable molecules, such as collagen fibrils, myofilaments, and polarized microtubule bundles. SHG imaging is therefore emerging as a novel approach for studying processes such as the physiopathological remodelling of the collagen matrix and myofibrillogenesis in intact tissue. THG does not require a non-centrosymmetric system; however no signal can be obtained from a homogeneous medium. THG imaging therefore provides maps of sub-micrometer heterogeneities (interfaces, inclusions) in unstained samples, and can be used as a general purpose structural imaging tool. Recent studies showed that this technique can be used to image embryo development in small organisms and to characterize the accumulation of large lipid bodies in specialized cells. SHG and THG microscopy both rely on femtosecond laser technology and are easily combined with two-photon microscopy. (10.1051/medsci/20062210845)
DOI : 10.1051/medsci/20062210845
Conformation of the c552:aa3 electron transfer complex in Paracoccus denitrificans studied by EPR on oriented samples
- Lipowski Gérard
- Liebl Ursula
- Guigliarelli Bruno
- Nitschke Wolfgang
- Schoepp-Cothenet Barbara
FEBS Letters, Wiley , 2006, 580 (25), pp.5988 . The EPR spectral parameters of aa3 oxidase and cyt c552 from Paracoccus denitrificans were studied in purified oxidase and enriched cyt c552. The orientation of the g-tensors of hemes a and c552 were determined on partially ordered membranes, enriched cyt c552 and a c552:aa3 subcomplex. The known correlation of g-tensor to molecular axes in histidine/methionine ligated hemes permits us to position cyt c552 with respect to the parent membrane. Taken together with previous data on the interaction surface between aa3 oxidase and cyt c552, these results allow us to arrive at a single conformation for the c552:aa3 electron transfer complex. Cop. 2006 Federation of European Biochemical Societies. (10.1016/j.febslet.2006.09.038)
DOI : 10.1016/j.febslet.2006.09.038
Single Lanthanide-doped Oxide Nanoparticles as Donors in Fluorescence Resonance Energy Transfer Experiments
- Casanova Didier
- Giaume D.
- Gacoin Thierry
- Boilot Jean-Pierre
- Alexandrou Antigoni
Journal of Physical Chemistry B, American Chemical Society , 2006, 110(39), pp.19264-19270 .
Photoinduced electron transfer from a novel nanotrigger addressed to the NADPH site within the endothelial NO-synthase to the flavin moieties of the protein
- Beaumont Edward
- Robin Anne-Claire
- Berka Vladimir
- Tsai Ah-Lim
- Blanchard-Desce Mireille
- Lambry Jean-Christophe
- Slama-Schwok Anny
Nitric Oxide: Biology and Chemistry, Elsevier , 2006, 14 (4), pp.14-15 . We developed a new selective molecular tool to trigger enzymatic activity in a synchronous manner and monitor the sequence of the kinetic events by ultra-fast transient spectroscopy. Our approach is based on a synthetic nanotrigger addressing a selected site within proteins, namely the conserved NADPH binding site common to many enzymes involved in bioreductive processes [1]. The nanotrigger combines a "docking" subunit responsible for the recognition of NADPH sites within proteins and a "chromophoric" subunit responsive to light excitation and able to transfer electrons to the flavin moieties of proteins. We present the first spectroscopic data on such a nanotrigger [1] in the presence of the reductase domain of the endothelial nitric oxide synthase eNOSred. (10.1016/j.niox.2006.04.050)
DOI : 10.1016/j.niox.2006.04.050
Endothelial nitric oxide synthase reduces nitrite anions to NO under anoxia
- Gautier Clément
- van Faassen E.
- Mikula I.
- Martasek P.
- Slama-Schwok Anny
Biochemical and Biophysical Research Communications, Elsevier , 2006, 341 (3), pp.816-821 . In this work, we demonstrate that endothelial nitric oxide synthase is capable of anoxic reduction of nitrite anions to nitric oxide at physiological pH by absorption and EPR spectroscopy and electrochemical measurements. The nitrite reduction is achieved at the oxygenase domain of the protein and proceeds even in the absence of the tetrahydrobiopterin cofactor. The nitrite pathway increases by sixfold the NO production with respect to the regular arginine pathway under hypoxia, which is largely blocked. Therefore, basal levels of NO release could be sustained by anoxic nitrite reduction. The reaction suggests a new pathway for fast NO delivery under hypoxia, precisely when the vasodilating properties of nitric oxide are most needed. (c) 2006 Elsevier Inc. All rights reserved. (10.1016/j.bbrc.2006.01.031)
DOI : 10.1016/j.bbrc.2006.01.031
Nouvelle approche des fibroses par microscopie multiphotonique avec génération de second harmonique [New approach of fibrosis by multiphoton microscopy with second harmonic generation]
- Hernest Monica
- Pena Ana-Maria
- Strupler Mathias
- Beaurepaire Emmanuel
- Martin Jean-Louis
- Schanne-Klein Marie-Claire
- Tharaux Pierre-Louis
Médecine/Sciences, EDP Sciences , 2006, 22 (10), pp.820-821 . La fibrose est une réponse adaptative pathologique qui détruit non spécifiquement les tissus. Il s'agit d'un processus universel de réparation des tissus qui survient en réaction à de nombreux types d'agressions telles les contraintes mécaniques, les brûlures, les radiations ionisantes, l'ischémie, l'inflammation. Ces agressions concourent de manière intriquée à la physiopathologie des maladies infectieuses, tumorales ou auto-immunes, de l'hypertension artérielle et des maladies cardio-vasculaires. Le terme de fibrose décrit précisément l'accumulation nouvelle de protéines de la matrice extra-cellulaire selon un arrangement spatial fibrillaire caractéristique. Il s'agit essentiellement de molécules de collagènes de type I et III (voire de type II, V ou XI) synthétisées sous forme de triples hélices elles-mêmes assemblées en fibrilles par les cellules fibroblastiques. L'apparition des collagènes fibrillaires marque un changement qualitatif et quantitatif de composition des collagènes des tissus. Réciproquement, ces changements de la matrice extracellulaire influencent le phénotype des cellules qui y résident. Ainsi dans le rein normal, le collagène de type I n'existe que dans l'adventice artériel. Son apparition au sein des autres structures de cet organe marque une fibrose tubulo-interstitielle qui constitue le meilleur marqueur pronostic défavorable d'une évolution vers l'insuffisance rénale terminale, et ce quelle que soit la maladie causale. Ainsi, comme lors des fibroses compliquant les hépatopathies et les pneumopathies chroniques, les séquelles de brûlures ou d'abrasions cutanées-muqueuses ou encore le remodelage cardiaque et vasculaire, le réarrangement de la géométrie de la matrice extracellulaire altère l'organisation fonctionnelle du tissu considéré. De ce fait, ce processus de réparation a des effets fonctionnels délétères qui constituent un enjeu médical majeur. Les fibrilles de collagène ont des capacités d'auto-assemblage qui sont aussi catalysées et stabilisées ou au contraire empêchées par les enzymes de la matrice extracellulaire. Le développement de la fibrose ou sa régression dépend donc ainsi du bilan des équilibres biologiques de ces mécanismes. Il est donc crucial de caractériser les changements extracellulaires et cellulaires qui font du restutio ad integrum de l'architecture et de la fonction tissulaire un défi biomédical. (10.1051/medsci/20062210820)
DOI : 10.1051/medsci/20062210820
Role of the middle residue in the triple tryptophan electron transfer chain of DNA photolyase: ultrafast spectroscopy of a Trp→Phe mutant
- Lukacs Andras
- Eker A.P.M.
- Byrdin M.
- Villette Sandrine
- Pan J.
- Brettel K.
- Vos Marten H.
Journal of Physical Chemistry B, American Chemical Society , 2006, 110 (32), pp.15654-15658 .
Mechanisms involved in the swelling of erythrocytes caused by Pacific and Caribbean ciguatoxins
- Sauviat Martin-Pierre
- Boydron-Le Garrec Raphaële
- Masson Jean-Baptiste
- Lewis Richard L.
- Vernoux Jean-Paul
- Molgó Jordi
- Laurent Dominique
- Benoit Evelyne
Blood Cells, Molecules and Diseases, Elsevier , 2006, 36(1), pp.1-9 . The mechanisms underlying the swelling of frog red blood cells (RBC), induced by Pacific (P-CTX-1) and Caribbean (C-CTX-1) ciguatoxins (CTXs), were investigated by measuring the length, width and surface of their elliptic shape. P-CTX-1 (0.5 to 5 nM) and C-CTX-1 (1 nM) induced RBC swelling within 60 min. The CTXs-induced RBC swelling was blocked by apamin (1 μM) and by Sr2+ (1 mM). P-CTX-1-induced RBC swelling was prevented and inhibited by H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (27 μM), an inhibitor of soluble guanylate cyclase (sGC), and NOS blockade by NG methyl-l-arginine (l-NMA; 10 μM). Cytochalasin D (cytD, 10 μM) increased RBC surface and mimicked CTX effect but did not prevent the P-CTX-1-induced l-NMA-sensitive extra increase. Calculations revealed that P-CTX-1 and cytD increase RBC total surface envelop and volume. These data strongly suggest that the molecular mechanisms underlying CTXs-induced RBC swelling involve the NO pathway by an activation of the inducible NOS, leading to sGC activation which modulates intracellular cGMP and regulates L-type Ca2+ channels. The resulting increase in intracellular Ca2+ content, in turn, disrupts the actin cytoskeleton, which causes a water influx and triggers a Ca2+-activated K+ current through SK2 isoform channels. (10.1016/j.bcmd.2005.10.007)
DOI : 10.1016/j.bcmd.2005.10.007
Coupling between surface plasmons in subwavelength hole arrays
- Masson Jean-Baptiste
- Gallot Guilhem
Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society , 2006, 73, pp.121401 .
Ionic contrast terahertz near field imaging of axonal water fluxes
- Masson Jean-Baptiste
- Sauviat Martin-Pierre
- Martin Jean-Louis
- Gallot Guilhem
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2006, 103 (13), pp.4808-4812 .
Hydrophobic distal pocket affects NO-heme geminate recombination dynamics in dehaloperoxidase and H64V myoglobin
- Franzen S.
- Jasaitis Audrius
- Belyea J.
- Brewer S.
- Casey Romain
- Macfarlane A.
- Martin Jean-Louis
- Stanley R.
- Vos Marten H.
Journal of Physical Chemistry B, American Chemical Society , 2006, 110 (29), pp.14483 . The recombination dynamics of NO with dehaloperoxidase ( DHP) from Amphitrite ornata following photolysis were measured by femtosecond time- resolved absorption spectroscopy. Singular value decomposition ( SVD) analysis reveals two important basis spectra. The first SVD basis spectrum reports on the population of photolyzed NO molecules and has the appearance of the equilibrium difference spectrum between the deoxy and NO forms of DHP. The first basis time course has two kinetic components with time constants of tau(11) approximate to 9 ps and tau(12) approximate to 50 ps that correspond to geminate recombination. The fast geminate process tau(11) arises from a contact pair with the heme iron in a bound state with S) 3/2 spin. The slow geminate process tau(12) corresponds to the recombination from a more remote docking site > 3 angstrom from the heme iron with the greater barrier corresponding to a S) 5/ 2 spin state. The second SVD basis spectrum represents a time- dependent Soret band shift indicative of heme photophysical processes and protein relaxation with time constants of tau(21) approximate to 3 ps and tau(22) approximate to 17 ps, respectively. A comparison between the more rapid rate constant of the slow geminate phase in DHP- NO and horse heart myoglobin ( HHMbNO) or sperm whale myoglobin ( SWMbNO) suggests that protein interactions with photolyzed NO are weaker in DHP than in the wild- type MbNOs, consistent with the hydrophobic distal pocket of DHP. The slower protein relaxation rate tau(22) in DHP- NO relative to HHMbNO implies less effective trapping in the docking site of the distal pocket and is consistent with a greater yield for the fast geminate process. The trends observed for DHP- NO also hold for the H64V mutant of SWMb ( H64V MbNO), consistent with a more hydrophobic distal pocket for that protein as well. We examine the influence of solution viscosity on NO recombination by varying the glycerol content in the range from 0% to 90% ( v/ v). The dominant effect of increasing viscosity is the increase of the rate of the slow geminate process, tau(12), coupled with a population decrease of the slow geminate component. Both phenomena are similar to the effect of viscosity on wild- type Mb due to slowing of protein relaxation resulting from an increased solution viscosity and protein surface dehydration. (10.1021/jp056790m)
DOI : 10.1021/jp056790m
Measuring the dynamics of circular dichroism in a pump-probe experiment with a Babinet-Soleil compensator
- Niezborala Claire
- Hache François
Journal of the Optical Society of America B, Optical Society of America , 2006, 23 (11), pp.2418 . Circular dichroism contains rich information on the conformation of molecules and, in particular, of biomolecules, and measuring its variation in a pump-probe experiment is very promising but also very challenging. We propose a new technique to measure pump-induced variation of the circular dichroism, which is based on the measurement of the probe ellipticity and its variation with the pump. This technique has the advantage that it does not require modulation of the probe polarization, which allows modulation of the pump intensity. We show theoretically and demonstrate experimentally that this technique is very sensitive and user friendly. We also show that it can be used to measure pump-induced change in the optical rotation, allowing for a complete characterization of pump-induced optical activity. Cop. 2006 Optical Society of America. (10.1364/JOSAB.23.002418)
DOI : 10.1364/JOSAB.23.002418
Parametric cascade downconverter for intense ultrafast mid-infrared generation beyond the Manley-Rowe limit
- Fraser James M.
- Ventalon Cathie
Applied optics, Optical Society of America , 2006, 45 (17), pp.4109-4113 . We propose a scheme to generate intense, ultrafast mid-infrared pulses with conversion efficiencies exceeding the upper bound for single-stage difference-frequency mixing as predicted by the Manley-Rowe relations. Finite-element fast Fourier transform simulations of the mixing process show that the parametric cascade downconverter generates 1.7 times more photons (at 10 μm ) than in the initial pump pulse (center wavelength of 1.48 μm , duration of 130 fs , and pulse energy of 50 μJ ), with negligible pulse spatial and temporal distortion. © 2006 Optical Society of America (10.1364/AO.45.004109)
DOI : 10.1364/AO.45.004109