Decrease In Electron Transport Activity Research Articles

Ionic copper strengthens the toxicity of tetrabromobisphenol A (TBBPA) to denitrification by decreasing substrate transport and electron transfer

Increasing electrical and electronic waste have raised concerns about the potential toxicity of brominated flame retardants (BFRs) and heavy metals (HMs). However, few studies have focused on the combined effect of BFRs and HMs on microorganisms, especially denitrifying bacteria, which have an essential role in N cycles and N2O emission. Herein, we investigate the combined effect of tetrabromobisphenol A (TBBPA) and Cu on model denitrifying bacteria. A further 24.5% decline in N removal efficiency was observed when 0.05 mg/L Cu were added into a denitrifying system containing 0.75 mg/L TBBPA. Further study demonstrated that Cu heightened the toxicity of TBBPA to denitrification via following aspects: (1) Cu stimulated EPS secretion induced by TBBPA during denitrification, blocked the transmembrane transport of glucose, which caused insufficient carbon substrate for bacteria growth and electron provision; (2) Cu further suppressed key denitrifying enzymes’ activity and down-regulated genes involving electron transport induced by TBBPA, led to the decrease of electron transport activity. Finally, the decrease of bacterial growth, insufficient electron donor, and lower electron transport activity caused the synergetic toxic effect of TBBPA and Cu on denitrification. Overall, the present study provides new insights into the combined effect of BFRs and HMs on microorganisms.

Self-Damaging Aerobic Reduction of Graphene Oxide by Escherichia coli: Role of GO-Mediated Extracellular Superoxide Formation.

Microbial reduction of graphene oxide (GO) under aerobic conditions is poorly understood despite its critical role in changing GO toxicity and environmental fate. Here we show that 20 mg/L GO interacts with the membrane-bound cytochrome c of E. coli in saline, shuttling electrons from the respiratory chain to extracellular molecular oxygen. This results in the formation of superoxide anions (O2•-), which in turn reduce GO in 30 min. The critical role of superoxide was demonstrated by impeding GO reduction upon addition of superoxide dismutase, or by carrying out experiments under strictly anaerobic conditions that preclude O2•- formation. Coating GO with bovine serum albumin also stopped GO reduction, which indicates the need for direct contact between GO and the cell membrane. Cell death was observed as a consequence of GO bioreduction. Apparently, electron shuttling by GO (via membrane contact) interrupts the respiratory chain and induces oxidative stress, as indicated by a 20% decrease in electron transport activity and an increase in intracellular reactive oxygen species. This novel antimicrobial mechanism could be relevant to assess GO stability and biocompatibility, and informs potential applications for microbial control.

New insight into the mechanism of mitochondrial cytochrome c function.

We investigate functional role of the P76GTKMIFA83 fragment of the primary structure of cytochrome c. Based on the data obtained by the analysis of informational structure (ANIS), we propose a model of functioning of cytochrome c. According to this model, conformational rearrangements of the P76GTKMIFA83 loop fragment have a significant effect on conformational mobility of the heme. It is suggested that the conformational mobility of cytochrome c heme is responsible for its optimal orientation with respect to electron donor and acceptor within ubiquinol–cytochrome c oxidoreductase (complex III) and cytochrome c oxidase (complex IV), respectively, thus, ensuring electron transfer from complex III to complex IV. To validate the model, we design several mutant variants of horse cytochrome c with multiple substitutions of amino acid residues in the P76GTKMIFA83 sequence that reduce its ability to undergo conformational rearrangements. With this, we study the succinate–cytochrome c reductase and cytochrome c oxidase activities of rat liver mitoplasts in the presence of mutant variants of cytochrome c. The electron transport activity of the mutant variants decreases to different extent. Resonance Raman spectroscopy (RRS) and surface-enhanced Raman spectroscopy (SERS) data demonstrate, that all mutant cytochromes possess heme with the higher degree of ruffling deformation, than that of the wild-type (WT) cytochrome c. The increase in the ruffled deformation of the heme of oxidized cytochromes correlated with the decrease in the electron transport rate of ubiquinol–cytochrome c reductase (complex III). Besides, all mutant cytochromes have lower mobility of the pyrrol rings and methine bridges, than WT cytochrome c. We show that a decrease in electron transport activity in the mutant variants correlates with conformational changes and reduced mobility of heme porphyrin. This points to a significant role of the P76GTKMIFA83 fragment in the electron transport function of cytochrome c.

Specific modification of two tryptophans within the nuclear-encoded subunits of bovine cytochrome c oxidase by hydrogen peroxide.

Hydrogen peroxide does more than react with the binuclear center of oxidized bovine cytochrome c oxidase and generate the well-characterized "peroxy" and "ferryl" forms. Hydrogen peroxide also inactivates detergent-solubilized cytochrome c oxidase in a time- and concentration-dependent manner. There is a 70-80% decrease of electron-transport activity, peroxidation of bound cardiolipin, modification of two nuclear-encoded subunits (IV and VIIc), and dissociation of approximately 60% of subunits VIa and VIIa. Modification of subunit VIIc and dissociation of subunit VIIa are coupled events that probably are responsible for the inactivation of cytochrome c oxidase. When cytochrome c oxidase is exposed to 500 microM hydrogen peroxide for 30 min at pH 7.4 and room temperature, subunits IV (modified up to 20%) and VIIc (modified up to 70%) each have an increased mass of 16 Da as detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrospray ionization mass spectrometry. In each case, the increased mass is caused by oxidation of a tryptophan (Trp19 within subunit VIIc and Trp48 within subunit IV), almost certainly due to formation of hydroxytryptophan. We conclude that hydrogen peroxide-induced oxidation of tryptophan and cardiolipin proceeds via the binuclear center since both modifications are prevented if the binuclear center is first blocked with cyanide. Bound cardiolipin and oxidized tryptophans are localized relatively far from the binuclear center (30-60 A); therefore, oxidation probably occurs by migration of a free radical generated at the binuclear center to these distal reaction sites.

Stability of Bovine Cytochrome c Oxidase as Studied After Exposure to High Hydrostatic Pressure

Structural and functional stability of bovine cytochrome c oxidase as a function of exposure to high hydrostatic pressure is reported. The pressure affects the stability of monomeric and dimeric enzyme quite differently. Exposure of the monomeric cytochrome c oxidase to pressures higher than 2.5 kbar causes dissociation of subunits III, VIa, VIb, VIIa with a 35-50% decrease in electron transport activity. Dimeric enzyme is more resistant to high hydrostatic pressure since subunits III and VIIa do not dissociate and the electron transport activity loss is minimal.

Enhanced Thermal Energy Dissipation Depending on Xanthophyll Cycle and D1 Protein Turnover in Iron-Deficient Maize Leaves Under High Irradiance

Pigment contents of chloroplasts and net photosynthetic rate were dramatically reduced in maize leaves suffering from iron deficiency. However, the reduction in photosynthesis was probably not caused by decreased contents of chlorophylls and carotenoids and by photon absorption; the primary limiting factor for photosynthesis may rather be the decrease of electron transport activity in photosystem 1. Iron-deficient leaves suffered serious acceptor-side photoinhibition, and more than 60 % of absorbed photons were dissipated, while less than 40 % was used in photochemical reaction. Thermal energy dissipation depending on xanthophyll cycle and D1 protein turnover was enhanced when acceptor-side photoinhibition occurred in iron-deficient maize leaves.

Oxidative damage to thylakoid proteins in water-stressed leaves of wheat (Triticum aestivum)

The production of reactive oxygen species in the chloroplast may increase under water deficit. To determine if this causes oxidative damage to the photosynthetic apparatus, we analyzed the accumulation of oxidatively damaged proteins in thylakoids of water-stressed wheat (Triticum aestivum L.) leaves. Water stress was imposed on 4-week-old plants by withholding watering for 10 days to reach a soil water potential of about - 2.0 MPa. In thylakoids of water-stressed leaves there was an increase in oxidative damage, particularly in polypeptides of 68, 54, 41 and 24 kDa. High molecular mass oxidized (probably cross-linked) proteins accumulated in chloroplasts of droughted leaves. Oxidative damage was associated with a substantial decrease in photosynthetic electron transport activity and photosystem II (PSII) efficiency (F v /F m ). Treatment of stressed leaves with L-galactono-1,4-lactone (GL) increased their ascorbic acid content and enhanced photochemical and non-photochemical quenching of chlorophyll fluorescence. GL reduced oxidative damage to photosynthetic proteins of droughted plants, but it reverted the decrease in electron transport activity and PSII efficiency only partially, suggesting that other factors also contributed to loss of photosystem activity in droughted plants. Increasing the ascorbic acid content of leaves might be an effective strategy to protect thylakoid membranes from oxidative damage in water-stressed leaves.

Photoinhibition in Euglena gracilis: Involvement of reactive oxygen species

Photoinhibition of isolated Euglena gracilis thylakoids was characterised by a drastic decline in PSII photochemistry, chlorophyll-a fluorescence and an enhanced degradation of the 32-kDa protein. The process of protein degradation, as shown by studies of [14C] atrazine binding, was clearly slower than the other events. The activity of PSI was not affected. Decrease of electron-transport activity and loss of herbicide binding were prevented in the presence of various antioxidants and enzymes which protect against free radicals; however, the protection was not total. The strongest effect was observed by addition of dimethylsulfoxide, a potent hydroxyl-radical (OH*) quencher. Furthermore, combinations of various protective substances were even more effective in reducing photoinhibition. Different reactive oxygen species, including H2O2, superoxide radicals and OH* radicals were obviously involved in photoinhibition. These results were confirmed by the addition of potential OH*-radical-generating substances. Simultaneous enhancement of OH*-radical formation and photoinhibitory damage were observed in these cases. The involvement of this highly toxic species could be shown directly by a colorimetric test, thus enabling its light-mediated formation during photoinhibition to be quantified for the first time. In all, the data indicate that a site in PSII is the origin of radical formation involved in photoinhibition and that H2O2 is an important precursor in the formation of hydroxyl-radicals.

Function of Photosynthetic Apparatus of Intact Wheat Leaves under High Light and Heat Stress and Its Relationship with Peroxidation of Thylakoid Lipids

Effects of high light and temperature stress on the structure and function of the photosynthetic apparatus of wheat (Triticum aestivum) were studied. There was a decrease in the electron transport activity of chloroplasts isolated from photoinhibited and heat-stressed leaves. Chlorophyll fluorescence was measured in photoinhibited and heat-stressed leaves and the decrease in variable fluorescence and variable to maximum fluorescence ratio of the stressed leaves indicated a loss in the quantum yield of photosynthesis. The decrease in electron transport activity was accompanied by an increase in peroxidation of thylakoid lipids. Lipid peroxidation indicated the oxidative degradation of polyunsaturated fatty acyl residues of the thylakoid lipids. A negative correlation was observed between electron transport activity and lipid peroxidation. The electron transport activity was completely lost as the peroxidation level reached a threshold equivalent to 0.6 micromoles malondialdehyde. The threshold of lipid peroxidation for complete loss of activity was the same for both photoinhibition and heat treatment, suggesting that the nature of the environmental stress may be less important with respect to the relationship between electron transport and lipid peroxidation. Thus, it seems likely that lipids are required for sustaining the photosynthetic activity under environmental stress, and a loss in activity is observed as the lipids are degraded either by high light or high temperature stress.

Alteration of Physiological Activity of Activated Macrophages through L-Arginine Metabolism

Our aim in this study was to define the effect of L‐arginine on macrophages (Mø) in relation to the decay of tumoricidal activity of activated Mø. We found that the activated M0 retained their cytotoxicity when cultured in L‐arginine‐deficient medium but not in conventional medium. Such a decline of tumoricidal activity was associated with increase of glucose consumption and concomitant lactate production, resulting in Mø death. Addition of glucose to the culture medium of activated Mø appeared to cause only a slight delay of the decrease of tumoricidal activity and Mø death. These events were also coincident with a decrease of electron transport activity in mitochondria. Cytological observation by electron microscopy clearly showed the structural alteration or destruction of mitochondria, which preceded the changes of other physiological and functional activities. These results demonstrate that the L‐arginine‐dependent cytolytic activity against tumor target cells also impairs M0 functions and ultimately induces Mø death, which is primarily mediated by the inhibition of mitochondrial activity.

Multifunctional Mode of Action of Substituted Nitrodiphenylethers in Scenedesmus Cells

Abstract Nitrodiphenylethers substituted with Cl, CF3, and other comparatively simple substituents are compared with respect to their primary effects on the photosynthetic apparatus. These are direct electron-transport inhibition, energy-transfer inhibition (of ATP synthesis), and pigment bleach­ ing, the latter accompanied by decrease of electron transport activity. Certain substituents and their positions at the diphenylether skeleton can be correlated with a particular influence on these phytotoxic effects. The unicellular alga, Scenedesmus, is an appropriate species to fumisch quantitative data on these primary herbicidal modes of action within a 24-h assay period.