Página 1 dos resultados de 327 itens digitais encontrados em 0.016 segundos

Characterization of the stimulus for reactive oxygen species generation in calcium-overloaded mitochondria

RODRIGUES, Fernando P.; PESTANA, Cezar R.; SANTOS, Guilherme A. Dos; PARDO-ANDREU, Gilberto L.; SANTOS, Antonio C.; UYEMURA, Sergio A.; ALBERICI, Luciane C.; CURTI, Carlos
Fonte: MANEY PUBLISHING Publicador: MANEY PUBLISHING
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.93%
We have used two different probes with distinct detection properties, dichlorodihydrofluorescein diacetate and Amplex Red/horseradish peroxidase, as well as different respiratory substrates and electron transport chain inhibitors, to characterize the reactive oxygen species (ROS) generation by the respiratory chain in calcium-overloaded mitochondria. Regardless of the respiratory substrate, calcium stimulated the mitochondrial generation of ROS, which were released at both the mitochondrial-matrix side and the extramitochondrial space, in a way insensitive to the mitochondrial permeability transition pores inhibitor cyclosporine A. In glutamate/malate-energized mitochondria, inhibition at complex I or complex III (ubiquinone cycle) similarly modulated ROS generation at either mitochondrial-matrix side or extramitochondrial space; this also occurred when the backflow of electrons to complex I in succinate-energized mitochondria was inhibited. On the other hand, in succinate-energized mitochondria the modulation of ROS generation at mitochondrial-matrix side or extra-mitochondrial space depends on the site of complex III which was inhibited. These results allow a straight comparison between the effects of different respiratory substrates and electron transport chain inhibitors on ROS generation at either mitochondrial-matrix side or extra-mitochondrial space in calcium-overloaded mitochondria.; FAPESP; CAPES; CNPq...

Análise dos níveis relativos de transcrição de genes antioxidantes e da cadeia de transporte de elétrons de Aspergillus fumigatus; Transcription relative levels analysis of Aspergillus fumigatus antioxidant and electrons transport chain genes

Rodrigues, Renata Vilela
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
85.96%

Modelling the effect of nonplanarity on charge transport along conjugated polymer chains

Correia, Helena M. G.; Ramos, Marta M. D.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.97%
Conjugated polymers show interesting properties that make them appropriated for nanoelectronics. Several studies of poly(p-phenylene vinylene) (PPV) have suggested that each polymer chain consists of several planar segments, with conjugation length of nanoscale dimension, linked by twists or kinks. A pronounced twist between two planar segments in a PPV chain not only causes loss of main-chain conjugation but it may also alter electron and hole mobility along the chain, which has further implications for the percolation of charge through the polymer film. We used self-consistent quantum molecular dynamics calculations to provide information on the electric field needed to move the injected charges (either electrons or holes) along the planar segments of PPV and to cross the twist between two planar segments perpendicular to each other. Field-dependent charge mobility was also estimated for conjugated segments of various lengths. Our results suggest that electrons can cross the twist between adjacent planar segments for lower applied electric fields than holes if there is no more than one electronic charge (electron or hole) on the PPV chain, otherwise similar fields are needed.; Fundação para a Ciência e a Tecnologia FCT) Programa Operacional “Ciência ...

Ascorbate Biosynthesis in Mitochondria Is Linked to the Electron Transport Chain between Complexes III and IV1

Bartoli, Carlos G.; Pastori, Gabriela M.; Foyer, Christine H.
Fonte: American Society of Plant Physiologists Publicador: American Society of Plant Physiologists
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
Ascorbic acid is synthesized from galactono-γ-lactone (GL) in plant tissues. An improved extraction procedure involving ammonium sulfate precipitation of membrane proteins from crude leaf homogenates yielded a simple, quick method for determining tissue activities of galactono-γ-lactone dehydrogenase (GLDH). Total foliar ascorbate and GLDH activity decreased with leaf age. Subcellular fractionation experiments using marker enzymes demonstrated that 80% of the total GLDH activity was located on the inner mitochondrial membrane, and 20% in the microsomal fraction. Specific antibody raised against potato (Solanum tuberosum L.) tuber GLDH recognized a 56-kD polypeptide in extracts from the mitochondrial membranes but failed to detect the equivalent polypeptide in microsomes. We demonstrate that isolated intact mitochondria synthesize ascorbate in the presence of GL. GL stimulated mitochondrial electron transport rates. The respiration inhibitor antimycin A stimulated ascorbate biosynthesis, while cyanide inhibited both respiration and ascorbate production. GL-dependent oxygen uptake was observed in isolated intact mitochondria. This evidence suggests that GLDH delivers electrons to the mitochondrial electron transport chain between complexes III and IV.

The NADPH oxidase of professional phagocytes—prototype of the NOX electron transport chain systems

Cross, Andrew R.; Segal, Anthony W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.8%
The NADPH oxidase is an electron transport chain in “professional” phagocytic cells that transfers electrons from NADPH in the cytoplasm, across the wall of the phagocytic vacuole, to form superoxide. The electron transporting flavocytochrome b is activated by the integrated function of four cytoplasmic proteins. The antimicrobial function of this system involves pumping K+ into the vacuole through BKCa channels, the effect of which is to elevate the vacuolar pH and activate neutral proteases. A number of homologous systems have been discovered in plants and lower animals as well as in man. Their function remains to be established.

Hydrogen is a preferred intermediate in the energy-conserving electron transport chain of Methanosarcina barkeri

Kulkarni, Gargi; Kridelbaugh, Donna M.; Guss, Adam M.; Metcalf, William W.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.96%
Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F420H2 dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However, Methanosarcina barkeri Δfpo mutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Δfrh mutants lacking the cytoplasmic F420-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Δfpo/Δfrh mutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless, M. barkeri does have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Δfrh mutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth of M. barkeri.

Identification of the 2-Hydroxyglutarate and Isovaleryl-CoA Dehydrogenases as Alternative Electron Donors Linking Lysine Catabolism to the Electron Transport Chain of Arabidopsis Mitochondria[W][OA]

Araújo, Wagner L.; Ishizaki, Kimitsune; Nunes-Nesi, Adriano; Larson, Tony R.; Tohge, Takayuki; Krahnert, Ina; Witt, Sandra; Obata, Toshihiro; Schauer, Nicolas; Graham, Ian A.; Leaver, Christopher J.; Fernie, Alisdair R.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.8%
This study indicates that Lys catabolism can directly channel electrons to the mitochondrial electron transport chain in addition to sustaining the operation of the tricarboxylic acid cycle under carbon-limiting conditions.

The Antimalarial Activities of Methylene Blue and the 1,4-Naphthoquinone 3-[4-(Trifluoromethyl)Benzyl]-Menadione Are Not Due to Inhibition of the Mitochondrial Electron Transport Chain

Ehrhardt, Katharina; Davioud-Charvet, Elisabeth; Ke, Hangjun; Vaidya, Akhil B.; Lanzer, Michael; Deponte, Marcel
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.88%
Methylene blue and a series of recently developed 1,4-naphthoquinones, including 3-[4-(substituted)benzyl]-menadiones, are potent antimalarial agents in vitro and in vivo. The activity of these structurally diverse compounds against the human malaria parasite Plasmodium falciparum might involve their peculiar redox properties. According to the current theory, redox-active methylene blue and 3-[4-(trifluoromethyl)benzyl]-menadione are “subversive substrates.” These agents are thought to shuttle electrons from reduced flavoproteins to acceptors such as hemoglobin-associated or free Fe(III)-protoporphyrin IX. The reduction of Fe(III)-protoporphyrin IX could subsequently prevent essential hemoglobin digestion and heme detoxification in the parasite. Alternatively, owing to their structures and redox properties, methylene blue and 1,4-naphthoquinones might also affect the mitochondrial electron transport chain. Here, we tested the latter hypothesis using an established system of transgenic P. falciparum cell lines and the antimalarial agents atovaquone and chloroquine as controls. In contrast to atovaquone, methylene blue and 3-[4-(trifluoromethyl)benzyl]-menadione do not inhibit the mitochondrial electron transport chain. A systematic comparison of the morphologies of drug-treated parasites furthermore suggests that the three drugs do not share a mechanism of action. Our findings support the idea that methylene blue and 3-[4-(trifluoromethyl)benzyl]-menadione exert their antimalarial activity as redox-active subversive substrates.

Initiation of Electron Transport Chain Activity in the Embryonic Heart Coincides with the Activation of Mitochondrial Complex 1 and the Formation of Supercomplexes

Beutner, Gisela; Eliseev, Roman A.; Porter, George A.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.8%
Mitochondria provide energy in form of ATP in eukaryotic cells. However, it is not known when, during embryonic cardiac development, mitochondria become able to fulfill this function. To assess this, we measured mitochondrial oxygen consumption and the activity of the complexes (Cx) 1 and 2 of the electron transport chain (ETC) and used immunoprecipitation to follow the generation of mitochondrial supercomplexes. We show that in the heart of mouse embryos at embryonic day (E) 9.5, mitochondrial ETC activity and oxidative phosphorylation (OXPHOS) are not coupled, even though the complexes are present. We show that Cx-1 of the ETC is able to accept electrons from the Krebs cycle, but enzyme assays that specifically measure electron flow to ubiquinone or Cx-3 show no activity at this early embryonic stage. At E11.5, mitochondria appear functionally more mature; ETC activity and OXPHOS are coupled and respond to ETC inhibitors. In addition, the assembly of highly efficient respiratory supercomplexes containing Cx-1, -3, and -4, ubiquinone, and cytochrome c begins at E11.5, the exact time when Cx-1 becomes functional activated. At E13.5, ETC activity and OXPHOS of embryonic heart mitochondria are indistinguishable from adult mitochondria. In summary...

Terminal branching of the respiratory electron transport chain in Neisseria meningitidis.

Yu, E K; DeVoe, I W
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.8%
The respiratory components of the envelope membrane preparation of Neisseria meningitidis were investigated. Oxidase activities were demonstrated in this fraction in the presence of succinic acid, reduced nicotinamide adenine dinucleotide, and ascorbate-N,N,N',N'-tetramethyl-p-phenylene-diamine (TMPD). Differences in the kinetics of inhibition by terminal oxidase inhibitors on the three oxidase activities indicated that ascorbate-TMPD oxidation involved only an azide-sensitive oxidase, whereas oxidation of the physiological substrates involved two oxidases, one of which was relatively azide resistant. Spectrophotometric studies revealed that ascorbate-TMPD donated its electrons exclusively to cytochrome o, whereas the physiological substrates were oxidized via both cytochromes o and a. The effects of class II inhibitors on the oxidases suggest terminal branching of the electron transport chain at the cytochrome b level. A model of the respiratory system in N. meningitidis is proposed.

Bond disorder and spinon heat transport in the $S=\tfrac{1}{2}$ Heisenberg spin chain compound Sr$_2$CuO$_3$: from clean to dirty limits

Mohan, A.; Beesetty, N. Sekhar; Hlubek, N.; Saint-Martin, R.; Revcolevschi, A.; Büchner, B.; Hess, C.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.92%
We investigate the effect of disorder on the heat transport properties of the $S=\tfrac{1}{2}$ Heisenberg chain compound Sr$_2$CuO$_3$ upon chemically substituting Sr by increasing concentrations of Ca. As Ca occupies sites outside but near the Cu-O-Cu spin chains, bond disorder, i.e. a spatial variation of the exchange interaction $J$, is expected to be realized in these chains. We observe that the magnetic heat conductivity ($\kappa_{\mathrm{mag}}$) due to spinons propagating in the chains is gradually but strongly suppressed with increasing amount of Ca, where the doping dependence can be understood in terms of increased scattering of spinons due to Ca-induced disorder. This is also reflected in the spinon mean free path which can be separated in a doping independent but temperature dependent scattering length due to spinon-phonon scattering, and a temperature independent but doping dependent spinon-defect scattering length. The latter spans from very large ($>$ 1300 lattice spacings) to very short ($\sim$ 12 lattice spacings) and scales with the average distance between two neighboring Ca atoms. Thus, the Ca-induced disorder acts as an effective defect within the spin chain, and the doping scheme allows to cover the whole doping regime between the clean and the dirty limits. Interestingly...

Bond disorder and breakdown of ballistic heat transport in the spin-1/2 antiferromagnetic Heisenberg chain as seen in Ca-doped SrCuO2

Hlubek, N.; Ribeiro, P.; Saint-Martin, R.; Nishimoto, S.; Revcolevschi, A.; Drechsler, S. -L.; Behr, G.; Trinckauf, J.; Hamann-Borrero, J. E.; Geck, J.; Büchner, B.; Hess, C.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.88%
We study the impact of a weak bond disorder on the spinon heat transport in the S=1/2 antiferromagnetic (AFM) Heisenberg chain material Sr_{1-x}Ca_xCuO_2. We observe a drastic suppression in the magnetic heat conductivity kappa_mag even at tiny disorder levels (i.e., Ca-doping levels), in stark contrast to previous findings for kappa_mag of S=1/2 two-dimensional square lattice and two-leg spin-ladder systems, where a similar bond disorder has no effect on kappa_mag. Hence, our results underpin the exceptional role of integrability of the S=1/2 AFM Heisenberg chain model and suggest that the bond disorder effectively destroys the ballistic nature of its heat transport. We further show that the suppression of kappa_mag is captured by an effective spinon-impurity scattering length, which exhibits the same doping dependence as the long-distance exponential decay length of the spin-spin correlation as determined by density-matrix renormalization group calculations.

Electron-like Fermi surface and in-plane anisotropy due to chain states in YBa$_2$Cu$_3$O$_{7-\delta}$ superconductors

Das, Tanmoy
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.88%
We present magneto-transport calculations for YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) materials to show that the electron-like metallic chain state gives both the negative Hall effect and in-plane anisotropic large Nernst signal. We show that the inevitable presence of the metallic 1D CuO chain layer lying between the CuO2 bilayers in YBCO renders an electron-like Fermi surface in the doping range as wide as p=0.05 to overdoping. With underdoping, a pseudogap opening in the CuO2 state reduces its hole-carrier contribution, and therefore the net electron-like quasiparticles dominate the transport properties, and a negative Hall resistance commences. We also show that the observation of in-plane anisotropy in the Nernst signal - which was taken as a definite evidence of the electronic nematic' pseudogap phase - is naturally explained by including the quasi-uniaxial' metallic chain state. Finally, we comment on how the chain state can also lead to electron-like quantum oscillations.; Comment: Submitted

Ballistic heat transport of quantum spin excitations as seen in SrCuO2

Hlubek, N.; Ribeiro, P.; Saint-Martin, R.; Revcolevschi, A.; Roth, G.; Behr, G.; Büchner, B.; Hess, C.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.88%
Fundamental conservation laws predict ballistic, i.e., dissipationless transport behaviour in one-dimensional quantum magnets. Experimental evidence, however, for such anomalous transport has been lacking ever since. Here we provide experimental evidence for ballistic heat transport in a S=1/2 Heisenberg chain. In particular, we investigate high purity samples of the chain cuprate SrCuO2 and observe a huge magnetic heat conductivity $\kappa_{mag}$. An extremely large spinon mean free path of more than a micrometer demonstrates that $\kappa_{mag}$ is only limited by extrinsic scattering processes which is a clear signature of ballistic transport in the underlying spin model.

Scaling of electrical and thermal conductivities in an almost integrable chain

Huang, Y.; Karrasch, C.; Moore, J. E.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.95%
Many low-dimensional materials are well described by integrable one-dimensional models such as the Hubbard model of electrons or the Heisenberg model of spins. However, the small perturbations to these models required to describe real materials are expected to have singular effects on transport quantities: integrable models often support dissipationless transport, while weak non-integrable terms lead to finite conductivities. We use matrix-product-state methods to obtain quantitative values of spin/electrical and thermal conductivities in an almost integrable gapless chain (an XXZ spin chain with staggered fields, or equivalently a spinless fermion chain with staggered on-site potentials). The results at low temperatures validate a scaling theory based on bosonization.

Zero-frequency transport properties of one dimensional spin-1/2 systems

Heidrich-Meisner, F.; Honecker, A.; Cabra, D. C.; Brenig, W.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.93%
We report a detailed analysis of the Drude weights for both thermal and spin transport in one dimensional spin-1/2 systems by means of exact diagonalization and analytic approaches at finite temperatures. Transport properties are studied first for the integrable XXZ model and second for various non-integrable systems such as the dimerized chain, the frustrated chain, and the spin ladder. We compare our results obtained by exact diagonalization and mean-field theory with the Bethe ansatz, bosonization and other numerical studies in the case of the anisotropic Heisenberg model both in the gapless and gapped regime. In particular, we find indications that the Drude weight for spin transport is finite in the thermodynamic limit for the isotropic chain. For the non-integrable models, a finite-size analysis of the numerical data for the Drude weights is presented covering the entire parameter space of the dimerized and frustrated chain. We also discuss which conclusions can be drawn from bosonization regarding the question whether the Drude weights are finite or not. One of our main results is that the Drude weights vanish in the thermodynamic limit for non-integrable models.; Comment: 19 pages REVTeX4 including 16 figures; final version to appear in Phys. Rev. B; minor changes

Incoherent transport induced by a single static impurity in a Heisenberg chain

Barisic, O. S.; Prelovsek, P.; Metavitsiadis, A.; Zotos, X.