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Redox Homeostasis (redox + homeostasi)
Selected AbstractsKnockout of major leaf ferredoxin reveals new redox-regulatory adaptations in Arabidopsis thalianaPHYSIOLOGIA PLANTARUM, Issue 3 2008Ingo Voss Ferredoxins are the major distributors for electrons to the various acceptor systems in plastids. In green tissues, ferredoxins are reduced by photosynthetic electron flow in the light, while in heterotrophic tissues, nicotinamide adenine dinucleotide (reduced) (NADPH) generated in the oxidative pentose-phosphate pathway (OPP) is the reductant. We have used a Ds -T-DNA insertion line of Arabidopsis thaliana for the gene encoding the major leaf ferredoxin (Fd2, At1g60950) to create a situation of high electron pressure in the thylakoids. Although these plants (Fd2-KO) possess only the minor fraction of leaf Fd1 (At1g10960), they grow photoautotrophically on soil, but with a lower growth rate and less chlorophyll. The more oxidized conditions in the stroma due to the formation of reactive oxygen species are causing a re-adjustment of the redox state in these plants that helps them to survive even under high light. Redox homeostasis is achieved by regulation at both, the post-translational and the transcriptional level. Over-reduction of the electron transport chain leads to increased transcription of the malate-valve enzyme NADP-malate dehydrogenase (MDH), and the oxidized stroma leads to an increased transcription of the OPP enzyme glucose-6-P dehydrogenase. In isolated spinach chloroplasts, oxidized conditions give rise to a decreased activation state of NADP-MDH and an activation of glucose-6-P dehydrogenase even in the light. In Fd2-KO plants, NADPH-requiring antioxidant systems are upregulated. These adjustments must be caused by plastid signals, and they prevent oxidative damage under rather severe conditions. [source] Chromosomal antioxidant genes have metal ion-specific roles as determinants of bacterial metal toleranceENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Joe J. Harrison Summary Microbiological metal toxicity involves redox reactions between metal species and cellular molecules, and therefore, we hypothesized that antioxidant systems might be chromosomal determinants affecting the susceptibility of bacteria to metal toxicity. Here, survival was quantified in metal ion-exposed planktonic cultures of several Escherichia coli strains, each bearing a mutation in a gene important for redox homeostasis. This characterized ,250 gene,metal combinations and identified that sodA, sodB, gor, trxA, gshA, grxA and marR have distinct roles in safeguarding or sensitizing cells to different toxic metal ions (Cr2O72,, Co2+, Cu2+, Ag+, Zn2+, AsO2,, SeO32, or TeO32,). To shed light on these observations, fluorescent sensors for reactive oxygen species (ROS) and reduced thiol (RSH) quantification were used to ascertain that different metal ions exert oxidative toxicity through disparate modes-of-action. These oxidative mechanisms of metal toxicity were categorized as involving ROS and thiol-disulfide chemistry together (AsO2,, SeO32,), ROS predominantly (Cu2+, Cr2O72,) or thiol-disulfide chemistry predominantly (Ag+, Co2+, Zn2+, TeO32,). Corresponding to this, promoter- luxCDABE fusions showed that toxic doses of different metal ions up- or downregulate the transcription of gene sets marking distinct pathways of cellular oxidative stress. Altogether, our findings suggest that different metal ions are lethal to cells through discrete pathways of oxidative biochemistry, and moreover, indicate that chromosomally encoded antioxidant systems may have metal ion-specific physiological roles as determinants of bacterial metal tolerance. [source] Hydroperoxide reduction by thioredoxin-specific glutathione peroxidase isoenzymes of Arabidopsis thalianaFEBS JOURNAL, Issue 24 2006Aqib Iqbal Arabidopsis thaliana contains eight glutathione peroxidase (GPX) homologs (AtGPX1,8). Four mature GPX isoenzymes with different subcellular distributions, AtGPX1, -2, -5 and -6, were overexpressed in Escherichia coli and characterized. Interestingly, these recombinant proteins were able to reduce H2O2, cumene hydroperoxide, phosphatidylcholine and linoleic acid hydroperoxides using thioredoxin but not glutathione or NADPH as an electron donor. The reduction activities of the recombinant proteins with H2O2 were 2,7 times higher than those with cumene hydroperoxide. Km values for thioredoxin and H2O2 were 2.2,4.0 and 14.0,25.4 µm, respectively. These finding suggest that GPX isoenzymes may function to detoxify H2O2 and organic hydroperoxides using thioredoxin in vivo and may also be involved in regulation of the cellular redox homeostasis by maintaining the thiol/disulfide or NADPH/NADP balance. [source] Mycothiol-dependent proteins in actinomycetesFEMS MICROBIOLOGY REVIEWS, Issue 3 2007Mamta Rawat Abstract The pseudodisaccharide mycothiol is present in millimolar levels as the dominant thiol in most species of Actinomycetales. The primary role of mycothiol is to maintain the intracellular redox homeostasis. As such, it acts as an electron acceptor/donor and serves as a cofactor in detoxification reactions for alkylating agents, free radicals and xenobiotics. In addition, like glutathione, mycothiol may be involved in catabolic processes with an essential role for growth on recalcitrant chemicals such as aromatic compounds. Following a little over a decade of research since the discovery of mycothiol in 1994, we summarize the current knowledge about the role of mycothiol as an enzyme cofactor and consider possible mycothiol-dependent enzymes. [source] Transcriptional profiling of the Candida albicans Ssk1p receiver domain point mutants and their virulenceFEMS YEAST RESEARCH, Issue 5 2008Veena Menon Abstract The Ssk1p response regulator of Candida albicans is required for oxidant adaptation, survival in human neutrophils, and virulence in a disseminated murine model of candidiasis. We have previously shown that the amino acid residues D556 and D513 of the Ssk1p receiver domain are critical to the Ssk1p in oxidant stress adaptation and morphogenesis. Herein, transcriptional profiling is used to explain the oxidant sensitivity and morphogenesis defect of two point mutants (D556N and D513K, respectively) compared with a WT strain. In the D556N mutant, during oxidative stress (5 mM H2O2), a downregulation of genes associated with redox homeostasis and oxidative stress occurred, which accounted for about 5% of all gene changes, including among others, SOD1 (superoxide dismutase), CAP1 (required for some types of oxidant stress), and three genes encoding glutathione biosynthesis proteins (GLR1, GSH1, and GSH2). Mutant D513K was not sensitive to peroxide but was impaired in its yeast $/to hyphal transition. We noted downregulation of genes associated with morphogenesis and cell elongation. Virulence of each mutant was also evaluated in a rat vaginitis model of candidiasis. Clearance of an SSK1 null and the D556N mutants from the vaginal canal was significantly greater than wild type or the D513K mutant, indicating that a change in a single amino acid of the Ssk1p alters the ability of this strain to colonize the rat vaginal mucosa. [source] MBSJ MCC Young Scientist Award 2009 REVIEW: Structural basis of protein disulfide bond generation in the cellGENES TO CELLS, Issue 9 2010Kenji Inaba The formation of protein disulfide bonds is an oxidative reaction that is crucial for the folding and maturation of many secreted and membrane proteins. Both prokaryotic and eukaryotic cells possess various disulfide oxidoreductases and redox-active cofactors to accelerate this oxidative reaction in a correct manner. Crystal or solution structures have been solved for some of the oxidoreductases in the past 10 years, leading to remarkable progress in the field of thiol-based redox cell biology. Consequently, structural and mechanistic similarities in the disulfide bond formation pathways have been uncovered. This review highlights the molecular basis of the elaborate oxidative systems operating in the Escherichia coli periplasm, the endoplasmic reticulum lumen and the mitochondrial intermembrane space. The accumulated knowledge provides important insights into how protein and redox homeostasis are maintained in the cell. [source] Proposed mechanism of inactivating Escherichia coli O157:H7 by ultra-high pressure in combination with tert -butylhydroquinoneJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008A.S. Malone Abstract Aims:, Investigating mechanisms of lethality enhancement when Escherichia coli O157:H7, and selected E. coli mutants, were exposed to tert -butylhydroquinone (TBHQ) during ultra-high pressure (UHP) treatment. Methods and Results:,Escherichia coli O157:H7 EDL-933, and 14 E. coli K12 strains with mutations in selected genes, were treated with dimethyl sulfoxide solution of TBHQ (15,30 ppm), and processed with UHP (400 MPa, 23 ± 2°C for 5 min). Treatment of wild-type E. coli strains with UHP alone inactivated 2·4,3·7 log CFU ml,1, whereas presence of TBHQ increased UHP lethality by 1·1,6·2 log CFU ml,1; TBHQ without pressure was minimally lethal (0,0·6 log reduction). Response of E. coli K12 mutants to these treatments suggests that iron,sulfur cluster-containing proteins ([Fe,S]-proteins), particularly those related to the sulfur mobilization (SUF system), nitrate metabolism, and intracellular redox potential, are critical to the UHP,TBHQ synergy against E. coli. Mutations in genes maintaining redox homeostasis and anaerobic metabolism were associated with UHP,TBHQ resistance. Conclusions:, The redox cycling activity of cellular [Fe,S]-proteins may oxidize TBHQ, potentially leading to the generation of bactericidal reactive oxygen species. Significance and Impact of the Study:, A mechanism is proposed for the enhanced lethality of UHP by TBHQ against E. coli O157:H7. The results may benefit food processors using UHP,based preservation, and biologists interested in piezophilic micro-organisms. [source] Current Opinions on the Functions of Tocopherol Based on the Genetic Manipulation of Tocopherol Biosynthesis in PlantsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2008Yin Li Abstract As a member of an important group of lipid soluble antioxidants, tocopherols play a paramount role in the daily diet of humans and animals. Recently, genes required for tocochromanol biosynthesis pathway have been identified and cloned with the help of genomics-based approaches and molecular manipulation in the model organisms: Arabidopsis thaliana and Synechocystis sp. PCC 6803. At the basis of these foundations, genetic manipulation of tocochromanol biosynthesis pathway can give rise to strategies that enhance the level of tocochromanol content or convert the constitution of tocochromanol. In addition, genetic manipulations of the tocochromanol biosynthesis pathway provide help for the study of the function of tocopherol in plant systems. The present article summarizes recent advances and pays special attention to the functions of tocopherol in plants. The roles of tocopherol in the network of reactive oxygen species, antioxidants and phytohormones to maintain redox homeostasis and the functions of tocopherol as a signal molecule in chloroplast-to-nucleus signaling to regulate carbohydrate metabolism are also discussed. [source] Altered free radical metabolism in acute mountain sickness: implications for dynamic cerebral autoregulation and blood,brain barrier functionTHE JOURNAL OF PHYSIOLOGY, Issue 1 2009D. M. Bailey We tested the hypothesis that dynamic cerebral autoregulation (CA) and blood,brain barrier (BBB) function would be compromised in acute mountain sickness (AMS) subsequent to a hypoxia-mediated alteration in systemic free radical metabolism. Eighteen male lowlanders were examined in normoxia (21% O2) and following 6 h passive exposure to hypoxia (12% O2). Blood flow velocity in the middle cerebral artery (MCAv) and mean arterial blood pressure (MAP) were measured for determination of CA following calculation of transfer function analysis and rate of regulation (RoR). Nine subjects developed clinical AMS (AMS+) and were more hypoxaemic relative to subjects without AMS (AMS,). A more marked increase in the venous concentration of the ascorbate radical (A,,), lipid hydroperoxides (LOOH) and increased susceptibility of low-density lipoprotein (LDL) to oxidation was observed during hypoxia in AMS+ (P < 0.05 versus AMS,). Despite a general decline in total nitric oxide (NO) in hypoxia (P < 0.05 versus normoxia), the normoxic baseline plasma and red blood cell (RBC) NO metabolite pool was lower in AMS+ with normalization observed during hypoxia (P < 0.05 versus AMS,). CA was selectively impaired in AMS+ as indicated both by an increase in the low-frequency (0.07,0.20Hz) transfer function gain and decrease in RoR (P < 0.05 versus AMS,). However, there was no evidence for cerebral hyper-perfusion, BBB disruption or neuronal,parenchymal damage as indicated by a lack of change in MCAv, S100, and neuron-specific enolase. In conclusion, these findings suggest that AMS is associated with altered redox homeostasis and disordered CA independent of barrier disruption. [source] Dicer ablation in oligodendrocytes provokes neuronal impairment in mice,ANNALS OF NEUROLOGY, Issue 6 2009Daesung Shin PhD Objective MicroRNAs (miRNAs) regulate gene expression and have many roles in the brain, but a role in oligodendrocyte (OL) function has not been demonstrated. Methods A Dicer floxed conditional allele was crossed with the proteolipid protein promoter-driven inducible Cre allele to generate inducible, OL-specific Dicer -floxed mice. Results OL-specific Dicer mutants show demyelination, oxidative damage, inflammatory astrocytosis and microgliosis in the brain, and eventually neuronal degeneration and shorter lifespan. miR-219 and its target ELOVL7 (elongation of very long chain fatty acids protein 7) were identified as the main molecular components that are involved in the development of the phenotype in these mice. Overexpressing ELOVL7 results in lipid accumulation, which is suppressed by miR-219 co-overexpression. In Dicer mutant brain, excess lipids accumulate in myelin-rich brain regions, and the peroxisomal ,-oxidation activity is dramatically reduced. Interpretation Postnatal Dicer ablation in mature OLs results in inflammatory neuronal degeneration through increased demyelination, lipid accumulation, and peroxisomal and oxidative damage, and therefore indicates that miRNAs play an essential role in the maintenance of lipids and redox homeostasis in mature OLs that are necessary for supporting axonal integrity as well as the formation of compact myelin. Ann Neurol 2009;66:843,857 [source] Oxidative stress in SEPN1 -related myopathy: From pathophysiology to treatment,ANNALS OF NEUROLOGY, Issue 6 2009Sandrine Arbogast PhD Objective Mutations of the selenoprotein N gene (SEPN1) cause SEPN1 -related myopathy (SEPN1-RM), a novel early-onset muscle disorder formerly divided into four different nosological categories. Selenoprotein N (SelN) is the only selenoprotein involved in a genetic disease; its function being unknown, no treatment is available for this potentially lethal disorder. Our objective was to clarify the role of SelN and the pathophysiology of SEPN1-RM to identify therapeutic targets. Methods We established and analyzed an ex vivo model of SelN deficiency using fibroblast and myoblast primary cultures from patients with null SEPN1 mutations. DCFH assay, OxyBlot, Western blot, Fura-2, and cell survival studies were performed to measure intracellular oxidant activity, oxidative stress markers, calcium handling, and response to exogenous treatments. Results SelN-depleted cells showed oxidative/nitrosative stress manifested by increased intracellular oxidant activity (reactive oxygen species and nitric oxide) and/or excessive oxidation of proteins, including the contractile proteins actin and myosin heavy chain II in myotubes. SelN-devoid myotubes showed also Ca2+ homeostasis abnormalities suggesting dysfunction of the redox-sensor Ca2+ channel ryanodine receptor type 1. Furthermore, absence of SelN was associated with abnormal susceptibility to H2O2 -induced oxidative stress, demonstrated by increased cell death. This cell phenotype was restored by pretreatment with the antioxidant N-acetylcysteine. Interpretation SelN plays a key role in redox homeostasis and human cell protection against oxidative stress. Oxidative/nitrosative stress is a primary pathogenic mechanism in SEPN1-RM, which can be effectively targeted ex vivo by antioxidants. These findings pave the way to SEPN1-RM treatment, which would represent a first specific pharmacological treatment for a congenital myopathy. Ann Neurol 2009;65:677,686 [source] Structure of Arabidopsis chloroplastic monothiol glutaredoxin AtGRXcpACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Lenong Li Monothiol glutaredoxins (Grxs) play important roles in maintaining redox homeostasis in living cells and are conserved across species. Arabidopsis thaliana monothiol glutaredoxin AtGRXcp is critical for protection from oxidative stress in chloroplasts. The crystal structure of AtGRXcp has been determined at 2.4,Å resolution. AtGRXcp has a glutaredoxin/thioredoxin-like fold with distinct structural features that differ from those of dithiol Grxs. The structure reveals that the putative active-site motif CGFS is well defined and is located on the molecular surface and that a long groove extends to both sides of the catalytic Cys97. Structural comparison and molecular modeling suggest that glutathione can bind in this groove and form extensive interactions with conserved charged residues including Lys89, Arg126 and Asp152. Further comparative studies reveal that a unique loop with five additional residues adjacent to the active-site motif may be a key structural feature of monothiol Grxs and may influence their function. This study provides the first structural information on plant CGFS-type monothiol Grxs, allowing a better understanding of the redox-regulation mechanism mediated by these plant Grxs. [source] Renal glutathione transport: Identification of carriers, physiological functions, and controversiesBIOFACTORS, Issue 6 2009Lawrence H. Lash Abstract Glutathione (GSH) is an endogenous tripeptide composed of the amino acids L -glutamate, L -cysteine, and glycine. It is found in virtually all aerobic cells and plays critical roles in maintenance of cellular redox homeostasis and drug metabolism. An important component of its regulation is transport across biological membranes. Because GSH is a charged, hydrophilic molecule, transport occurs via catalysis by specific carrier proteins rather than by simple diffusion. Although it has been clearly understood that efflux of GSH across membranes such as the canalicular and sinusoidal plasma membranes in hepatocytes and the brush-border plasma membrane in renal proximal tubules is a key step in GSH turnover and interorgan metabolism, the existence and physiological functions of uptake of GSH across various epithelial plasma membranes has been subject to some debate. Besides transport across plasma membranes, GSH transport across intracellular membranes, most notably the mitochondrial inner membrane, has received some attention in recent years because of the importance of mitochondrial redox status and the mitochondrial GSH pool in cellular physiology and pathology. This commentary will focus on renal transport processes for GSH and will discuss some of the controversies that have existed and still seem to exist in the literature, specifically regarding uptake of intact GSH by basolateral membranes of renal proximal tubular cells and uptake of intact GSH by the mitochondrial inner membrane. © 2009 International Union of Biochemistry and Molecular Biology, Inc. [source] Differential effects of redox-cycling and arylating quinones on trans-plasma membrane electron transportBIOFACTORS, Issue 3 2008An S. Tan Abstract Cytotoxicity of quinones has been attributed to free radical generation and to arylation of cellular nucleophiles. For redox-cycling quinones, cell injury is associated with mitochondrial permeability transition, whereas arylating quinones directly depolarise the mitochondrial membrane and deplete ATP. Like mitochondrial electron transport, plasma membrane electron transport (PMET), plays a multifaceted role in cellular redox homeostasis but the effects of quinones on PMET are unknown. Here we investigate the effects of redox-cycling 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), arylating 1,4-benzoquinone (BQ) and mixed mechanism 2-methyl-1,4-naphthoquinone (MNQ) on PMET, viability and growth of P815 mouse mastocytoma cells. BQ and MNQ rapidly and extensively inhibited PMET as determined by WST-1 /mPMS reduction (IC50 3.5-5 ,Mat 30 min) whereas the effects of DMNQ were less pronounced. In contrast, MTT reduction (cytosolic NADH dehydrogenase activity over 30 min) was weakly inhibited by BQ (IC50 20 ,M) but not by MNQ or DMNQ and cell viability was unaffected. Inhibition of WST-1/mPMS reduction by BQ and MNQ but not DMNQ was fully reversed by NAC. Treatment with DMNQ, MNQ and to a lesser extent BQ inhibited cell proliferation as determined by MTT reduction at 48 h. The effects of BQ and MNQ were reversed by NAC through covalent bonding to BQ and MNQ, but not DMNQ. These results show that arylating quinones are more potent inhibitors of PMET than pure redox-cycling quinones, but that redox-cycling quinones are more cytotoxic. [source] Oxidoreductase macrophage migration inhibitory factor is simultaneously increased in leukocyte subsets of patients with severe sepsisBIOFACTORS, Issue 4 2008Lutz E. Lehmann M.D. Abstract The oxidoreductase Macrophage Migration Inhibitory Factor (MIF) is discussed as a promising target for immunomodulatory therapy in patients with severe sepsis. Moreover, MIF expresses tautomerase as well as thiol-protein oxidore-ductase activities and has a potential role in cellular redox homeostasis, apoptosis inhibition, endotoxin responsiveness as well as regulation of nuclear transcription factors. To further elucidate a potential role of intracellular MIF in severe sepsis, we assessed alterations of intracellular MIF content in peripheral blood leukocytes of patients with severe sepsis in comparison to healthy controls and non-septic patients after major surgery. Intracellular MIF was significantly elevated simultaneously in lymphocytes, B-cells, macrophages and granulocytes of patients with severe sepsis when compared to healthy control individuals (p < 0.05) and increased when compared to non-septic patients after major surgery. In parallel, plasma MIF levels were elevated in severe sepsis (p < 0.05). There was no difference of intracellular MIF in lymphocytes, B-cells, macrophages or granulocytes between surviving and non-surviving patients with severe sepsis (p > 0.05). However, in survivors LPS ex vivo stimulation increased MIF secretion but not in non-survivors of sepsis (p < 0.05). This finding underlines the role of intracellular MIF in inflammatory diseases. It suggests monitoring of intracellular MIF in further clinical and non-clinical research valuable. [source] Impact of oxidative stress on lung diseasesRESPIROLOGY, Issue 1 2009Hee Sun PARK ABSTRACT Reactive oxygen species (ROS) are products of normal cellular metabolism and are known to act as second messengers. Under physiological conditions, ROS participate in maintenance of cellular ,redox homeostasis' in order to protect cells against oxidative stress through various redox-regulatory mechanisms. Overproduction of ROS, most frequently due to excessive stimulation of either reduced nicotinamide adenine dinucleotide phosphate by cytokines or the mitochondrial electron transport chain and xanthine oxidase, results in oxidative stress. Oxidative stress is a deleterious process that leads to lung damage and consequently to various disease states. Knowledge of the mechanisms of ROS regulation could lead to the pharmacological manipulation of antioxidants in lung inflammation and injury. 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