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At least 19 recordsLinked to original sources
PubMed1992

Characterization of aliphatic amine 1,4-diazobicyclo (2,2,2) octane-induced stimulation of beet spinach thylakoid electron transport.

Electron transport activity of beet spinach thylakoids was enhanced in the presence of aliphatic amine, DABCO (1,4-diazobicyclo (2,2,2) octane), a hydrophilic proton trapping agent. The extent of stimulation was pH-dependent and similar to the effect of the uncoupler ammonium chloride on electron transport. The stimulation of whole-chain (H2O-->MV) electron transport activity was observed only at high (rate-saturating) light intensity. The light-induced proton uptake coupled to electron transport of thylakoid was also arrested by DABCO, suggesting that DABCO uncouples thylakoid phosphorylation by proton trapping.

Chloroplasts↗
PubMed2000

Chlororespiration and poising of cyclic electron transport. Plastoquinone as electron transporter between thylakoid NADH dehydrogenase and peroxidase.

Polypeptides encoded by plastid ndh genes form a complex (Ndh) which could reduce plastoquinone with NADH. Through a terminal oxidase, reduced plastoquinone would be oxidized in chlororespiration. However, isolated Ndh complex has low activity with plastoquinone and no terminal oxidase has been found in chloroplasts, thus the function of Ndh complex is unknown. Alternatively, thylakoid hydroquinone peroxidase could oxidize reduced plastoquinone with H(2)O(2). By immunoaffinity chromatography, we have purified the plastid Ndh complex of barley (Hordeum vulgare L.) to investigate the electron donor and acceptor specificity. A detergent-containing system was reconstructed with thylakoid Ndh complex and peroxidase which oxidized NADH with H(2)O(2) in a plastoquinone-dependent process. This system and the increases of thylakoid Ndh complex and peroxidase activities under photooxidative stress suggest that the chlororespiratory process consists of the sequence of reactions catalyzed by Ndh complex, peroxidase (acting on reduced plastoquinone), superoxide dismutase, and the non-enzymic one-electron transfer from reduced iron-sulfur protein (FeSP) to O(2). When FeSP is a component of cytochrome b(6).f complex or of the same Ndh complex, O(2) may be reduced with NADH, without requirement of light. Chlororespiration consumes reactive species of oxygen and, eventually, may decrease their production by lowering O(2) concentration in chloroplasts. The common plastoquinone pool with photosynthetic electron transport suggests that chlororespiratory reactions may poise reduced and oxidized forms of the intermediates of cyclic electron transport under highly fluctuating light intensities.

Ascorbate Peroxidases↗
PubMed1987

Secretory vesicle cytochrome b561: a transmembrane electron transporter.

The major function of cytochrome b561 is now clear. This transmembrane protein transports electrons across a secretory vesicle bilayer to supply electrons to monooxygenases inside the secretory vesicle. Cytochrome b561 has been localized not only to adrenergic secretory vesicles, where it supplies electrons to dopamine beta-hydroxylase, but also to peptidergic secretory vesicles that contain peptidyl alpha-amidating monooxygenase. Thus, one would expect to find cytochrome b561 in the membranes of all neuroendocrine cells that contain amidated peptide secretory products. In addition, its wide occurrence as an integral membrane protein of secretory vesicles may make it useful for investigation of vesicle biogenesis and turnover. One of the most important potential roles of cytochrome b561 is that it can be used as a model protein to investigate long-range biological electron transport. This cytochrome is a single polypeptide, which can be purified easily and reconstituted into a functional assembly. It also catalyzes an experimentally unambiguous transmembrane transport of electrons. A full molecular characterization of the structure and function of this cytochrome may provide insights into biological electron transfer which would otherwise be difficult or impossible to obtain.

Animals↗
PubMed1984

Studies on Tetrahymena microsomal electron transport systems: solubilization of microsomal electron transport enzymes involved in fatty acid desaturation.

Tetrahymena microsomes were solubilized with five different detergents and the effect on electron transport enzymes involved in fatty acid desaturation was studied. Cytochrome b560ms and NADPH-cytochrome c reductase were solubilized with a low concentration detergent (0.25%), in the order of sodium deoxycholate greater than Renex 690 greater than Triton X-100 greater than octylglucoside greater than sodium cholate, whereas all of these detergents at the high concentration (1%) could solubilize preferentially both enzymes (70-100%). Increasing the concentration of various detergents from 0.5 to 1.0% did not produce an incremental change in NADH-ferricyanide reductase solubilization. NADH-cytochrome c reductase system, which would be catalyzed by the cooperation action of NADH-ferricyanide and cytochrome b560ms, was relatively inactivated by all detergents. Compared to the other four detergents, octylglucoside has a much higher recovery of stearoyl-CoA desaturase activities in the supernatant. Our study suggests that octylglucoside may be more useful for the isolation in active form of cyanide-sensitive factor (CSF) from Tetrahymena microsomes.

Animals↗
PubMedDate not supplied

Production of reactive oxygen species in brain mitochondria: contribution by electron transport chain and non-electron transport chain sources.

Overwhelming evidence has accumulated indicating that oxidative stress is a crucial factor in the pathogenesis of neurodegenerative diseases. The major site of production of superoxide, the primary reactive oxygen species (ROS), is considered to be the respiratory chain in the mitochondria, but the exact mechanism and the precise location of the physiologically relevant ROS generation within the respiratory chain have not been disclosed as yet. Studies performed with isolated mitochondria have located ROS generation on complex I and complex III, respectively, depending on the substrates or inhibitors used to fuel or inhibit respiration. A more "physiological" approach is to address ROS generation of in situ mitochondria, which are present in their normal cytosolic environment. Hydrogen peroxide formation in mitochondria in situ in isolated nerve terminals is enhanced when complex I, complex III, or complex IV is inhibited. However, to induce a significant increase in ROS production, complex III and complex IV have to be inhibited by >70%, which raises doubts as to the physiological importance of ROS generation by these complexes. In contrast, complex I inhibition to a small degree is sufficient to enhance ROS generation, indicating that inhibition of complex I by approximately 25-30% observed in postmortem samples of substantia nigra from patients suffering from Parkinson's disease could be important in inducing oxidative stress. Recently, it has been described that a key Krebs cycle enzyme, alpha-ketoglutarate dehydrogenase (alpha-KGDH), is also able to produce ROS. ROS formation by alpha-KGDH is regulated by the NADH/NAD+ ratio, suggesting that this enzyme could substantially contribute to generation of oxidative stress due to inhibition of complex I. As alpha-KGDH is not only a generator but also a target of ROS, it is proposed that alpha-KGDH is a key factor in a vicious cycle by which oxidative stress is induced and promoted in nerve terminals.

Animals↗
PubMed1976

Electron transport in xanthine oxidase. A model for other biological electron transport chains.

Part of the catalytic function of xanthine oxidase (XO) involves the transfer of two electrons from a substrate to a molybdenum ion on the enzyme followed by equilibration of these electrons among other electron resting sites on the enzyme. The electrons are removed from the enzyme at a flavin by oxygen to form hydrogen peroxide. This paper considers mechanisms which allow the electrons to equilibrate between the different resting sites on the enzyme. The mechanisms are chosen to be consistent with known properties of the enzyme (relative reduction potentials, electron transfer rates, and the estimated separation of these resting sites). Tunneling appears to be a good candidate to account for most of the electron transport. It is shown that the XO electron transport system is similar in many respects to sections of mitochondrial electron transport chains and can serve as a nice model for parts of these more complicated biological electron transport systems.

Catalysis↗
PubMed2001

A strain of Synechocystis sp. PCC 6803 without photosynthetic oxygen evolution and respiratory oxygen consumption: implications for the study of cyclic photosynthetic electron transport.

Cyclic electron transport around photosystem (PS) I is believed to play a role in generation of ATP required for adaptation to stress in cyanobacteria and plants. However, elucidation of the pathway(s) of cyclic electron flow is difficult because of low rates of this electron flow relative to those of linear photosynthetic and respiratory electron transport. We have constructed a strain of Synechocystis sp. PCC 6803 that lacks both PSII and respiratory oxidases and that, consequently, neither evolves nor consumes oxygen. However, this strain is still capable of cyclic electron flow around PSI. The photoheterotrophic growth rate of this strain increased with light intensity up to an intensity of about 25 mumol photons m-2 s-1, supporting the notion that cyclic electron flow contributes to ATP generation in this strain. Indeed, the ATP-generating ability of PSI is demonstrated by the fact that the PSII-less oxidase-less strain is able to grow at much higher salt concentrations than a strain lacking PSI. A quinone electrode was used to measure the redox state of the plastoquinone pool in vivo in the various strains used in this study. In contrast to what is observed in chloroplasts, the plastoquinone pool was rather reduced in darkness and was oxidized in the light. This is in line with significant electron donation by respiratory pathways (NADPH dehydrogenase and particularly succinate dehydrogenase) in darkness. In the light, the pool becomes oxidized due to the presence of much more PSI than PSII. In the oxidase-less strains, the plastoquinone pool was very much reduced in darkness and was oxidized in the light by PSI. Photosystem II activity did not greatly alter the redox state of the plastoquinone pool. The results suggest that cyclic electron flow around PSI can contribute to generation of ATP, and a strain deficient in linear electron transport pathways provides an excellent model for further investigations of cyclic electron flow.

Adenosine Triphosphate↗
PubMed1966

Photosynthetic Electron Transport Chain of Chlamydomonas reinhardi VI. Electron Transport in Mutant Strains Lacking Either Cytochrome 553 or Plastocyanin.

A mutant strain of Chlamydomonas reinhardi, ac-206, lacks cytochrome 553, at least in an active and detectable form. Chloroplast fragments of this mutant strain are inactive in the photoreduction of NADP when the source of electrons is water, but they are active when the electron source is 2,6-dichlorophenolindophenol and ascorbate. The addition of either cytochrome 553 or plastocyanin, obtained from the wild-type strain, has no effect upon the photosynthetic activities of the mutant strain. Cells of the mutant strain lack both the soluble and insoluble forms of cytochrome 553, but they possess the mitochondrial type cytochrome c. Thus, the loss of cytochrome 553 appears to be specific.Another mutant strain, ac-208, lacks plastocyanin, or possesses it in an inactive and undetectable form. Chloroplast fragments of ac-208 are inactive in the photoreduction of NADP with either water or 2,6-dichlorophenolindophenol and ascorbate as electron donors. However, these reactions are restored upon the addition of plastocyanin. The addition of cytochrome 553 has no effect. The measurement of light-induced absorbance changes with ac-208 reveal that, in the absence of plastocyanin, light fails to sensitize the oxidation of cytochrome 553, but it will sensitize its reduction. However, the addition of plastocyanin restores the light-induced cytochrome oxidation.A third mutant strain, ac-208 (sup.) carries a suppressor mutation that partially restores the wild phenotype. This mutant strain appears to possess a plastocyanin that is less stable than that of the wild-type strain.The observations with the mutant strains are discussed in terms of the sequence of electron transport System II --> cytochrome 553 --> plastocyanin --> System I.

Journal Article↗
PubMed2004

Electron transport in bipyridinium films.

Bipyridinium dications are versatile building blocks for the assembly of functional materials. In particular, their reliable electrochemical response has encouraged the design of electroactive films. Diverse and elegant experimental strategies to coat metallic and semiconducting electrodes with bipyridinium compounds have, in fact, emerged over the past two decades. The resulting interfacial assemblies span from a few nanometers to several micrometers in thickness. They incorporate from a single molecular layer to large collections of entangled polymer chains. They transport electrons efficiently from the electrode surface to the film/solution interface and vice versa. Electron self-exchange between and the physical diffusion of the bipyridinium building blocks conspire in defining the charge transport properties of these fascinating electroactive assemblies. Often, the matrix of electron-deficient bipyridinium dications can be exploited to entrap electron-rich analytes. Electrostatic interactions promote the supramolecular association of the guests with the surface-confined host matrix. Furthermore, chromophoric sites can be coupled to the bipyridinium dications to produce photosensitive arrays capable of harvesting light and generating current. Thus, thorough investigations on the fundamental properties of these functional molecule-based materials can lead to promising applications in electroanalysis and solar energy conversion, while contributing to advances in the basic understanding of electron transport in interfacial assemblies.

Electrochemistry↗
PubMed2000

Theory of malignant cell transformation by superoxide fate coupled with cytoskeletal electron-transport and electron-transfer.

Signaling and tumor promoting functions have been experimentally assigned to the cytoskeleton, many of them linked to oxygen free radicals like superoxide. Superoxide and other reactive oxygen species (ROS) have been associated for many years with oncogenesis, and they are emerging as important signaling molecules connected to the classical signaling pathways, the cytoskeleton, the cell cycle control, and tumor initiation and promotion. Complex and multifunctional relationships between these entities are being discovered and attributed to specific protein-protein interactions. Theoretical analysis and experimental data indicate that small electronic currents may be carried by semiconduction electron transport along biopolymers. Therefore, it is proposed in this paper that the tumor-promoting effects mentioned above might be under control or modulation of these tiny electronic currents originated in relation to ROS and transported through the cytoskeletal actin microfilament network.

Cell Transformation, Neoplastic↗
PubMed2005

EPR study of electron transport in the cyanobacterium Synechocystis sp. PCC 6803: oxygen-dependent interrelations between photosynthetic and respiratory electron transport chains.

In this work, we investigated electron transport processes in the cyanobacterium Synechocystis sp. PCC 6803, with a special emphasis focused on oxygen-dependent interrelations between photosynthetic and respiratory electron transport chains. Redox transients of the photosystem I primary donor P700 and oxygen exchange processes were measured by the EPR method under the same experimental conditions. To discriminate between the factors controlling electron flow through photosynthetic and respiratory electron transport chains, we compared the P700 redox transients and oxygen exchange processes in wild type cells and mutants with impaired photosystem II and terminal oxidases (CtaI, CydAB, CtaDEII). It was shown that the rates of electron flow through both photosynthetic and respiratory electron transport chains strongly depended on the transmembrane proton gradient and oxygen concentration in cell suspension. Electron transport through photosystem I was controlled by two main mechanisms: (i) oxygen-dependent acceleration of electron transfer from photosystem I to NADP(+), and (ii) slowing down of electron flow between photosystem II and photosystem I governed by the intrathylakoid pH. Inhibitor analysis of P700 redox transients led us to the conclusion that electron fluxes from dehydrogenases and from cyclic electron transport pathway comprise 20-30% of the total electron flux from the intersystem electron transport chain to P700(+).

Electron Spin Resonance Spectroscopy↗
PubMed1995

Short note: are electron-transport and electron-transfer involved in intracellular signaling?

In this paper, the possibility of electron-transfer and subsequent electron transport across membrane proteins (ion channels) is studied with respect to the ion channel function. The electronic properties of the ionic channel protein interface with the electrolytes, and the properties of the same ion channel protein as a solid-state biopolymer are used as the physical basis to explain these elementary charge transport phenomena. It is proposed that, by means of the occurrence of those two processes, there can be electrons participating in the activation of the G-proteins and subsequent intracellular signaling. As another example, the same analysis is used to propose the involvement of electrons in the neuromodulation of the ionic channels.

Animals↗