Fe-superoxide Dismutase Research Articles

Cardiomyocyte diffusible redox mediators control Trypanosoma cruzi infection: role of parasite mitochondrial iron superoxide dismutase.

Chagas disease (CD), caused by the protozoa Trypanosoma cruzi, is a chronic illness in which parasites persist in the host-infected tissues for years. T. cruzi invasion in cardiomyocytes elicits the production of pro-inflammatory mediators [TNF-α, IL-1β, IFN-γ; nitric oxide (·NO)], leading to mitochondrial dysfunction with increased superoxide radical (O2·-), hydrogen peroxide (H2O2) and peroxynitrite generation. We hypothesize that these redox mediators may control parasite proliferation through the induction of intracellular amastigote programmed cell death (PCD). In this work, we show that T. cruzi (CL-Brener strain) infection in primary cardiomyocytes produced an early (24 h post infection) mitochondrial dysfunction with H2O2 generation and the establishment of an oxidative stress evidenced by FoxO3 activation and target host mitochondrial protein expression (MnSOD and peroxiredoxin 3). TNF-α/IL-1β-stimulated cardiomyocytes were able to control intracellular amastigote proliferation compared with unstimulated cardiomyocytes. In this condition leading to oxidant formation, an enhanced number of intracellular apoptotic amastigotes were detected. The ability of H2O2 to induce T. cruzi PCD was further confirmed in the epimastigote stage of the parasite. H2O2 treatment induced parasite mitochondrial dysfunction together with intra-mitochondrial O2·- generation. Importantly, parasites genetically engineered to overexpress mitochondrial Fe-superoxide dismutase (Fe-SODA) were more infective to TNF-α/IL-1β-stimulated cardiomyocytes with less apoptotic amastigotes; this result underscores the role of this enzyme in parasite survival. Our results indicate that cardiomyocyte-derived diffusible mediators are able to control intracellular amastigote proliferation by triggering T. cruzi PCD and that parasite Fe-SODA tilts the process toward survival as part of an antioxidant-based immune evasion mechanism.

Combined QM/MM and Monte Carlo study for redox leveling in Mn and Fe superoxide dismutase.

Superoxide dismutases (SOD) are vital enzymes for disproportionation of superoxide molecules in mammals. Despite the high similarity between the Mn-SOD and Fe-SOD, they are inactive if the metals in the active sites are exchanged. Here, we use DFT, QM/MM and Monte Carlo sampling to optimize the crystal structure and to calculate the mid-point potential for the native and substituted Mn/Fe-SOD. The optimized DFT and QM/MM structures of the Mn-SOD show a major conformational change for the conserved TYR34 compared to the X-ray structure. These changes reduce the distance between TYR34 and Mn ion to 2.59Å, which yields a lower reduction potential for the Mn. On contrary, there is no significant difference between optimized and crystal structures in the Fe-SOD. The calculated E m values starting from the DFT structures of the active sites show similar pattern, in good agreement with those observed experimentally. However, the calculated E m values starting with the QM/MM structures that include the whole protein are significantly higher due to the desolvation penalty. In addition, the pK a values for the water ligand in the reduced state Mn(II) and Fe(II) were calculated. The water pK a in Mn-SOD is higher than that in Fe-SOD by 3.5 pH units, which is similar to the shift measured experimentally. Finally, we investigated the role of HIS30 and the effect of its protonation state on the E m values.

Library of Seleno-Compounds as Novel Agents against Leishmania Species.

The in vitro leishmanicidal activities of a series of 48 recently synthesized selenium derivatives against Leishmania infantum and Leishmania braziliensis parasites were tested using promastigotes and intracellular amastigote forms. The cytotoxicity of the tested compounds for J774.2 macrophage cells was also measured in order to establish their selectivity. Six of the tested compounds (compounds 8, 10, 11, 15, 45, and 48) showed selectivity indexes higher than those of the reference drug, meglumine antimonate (Glucantime), for both Leishmania species; in the case of L. braziliensis, compound 20 was also remarkably selective. Moreover, data on infection rates and amastigote numbers per macrophage showed that compounds 8, 10, 11, 15, 45, and 48 were the most active against both Leishmania species studied. The observed changes in the excretion product profile of parasites treated with these six compounds were also consistent with substantial cytoplasmic alterations. On the other hand, the most active compounds were potent inhibitors of Fe superoxide dismutase (Fe-SOD) in the two parasite species considered, whereas their impact on human CuZn-SOD was low. The high activity, low toxicity, stability, low cost of the starting materials, and straightforward synthesis make these compounds appropriate molecules for the development of affordable antileishmanicidal agents.

Interactive effects of salt stress and Pseudomonas syringae pv. lachrymans infection in cucumber: Involvement of antioxidant enzymes, abscisic acid and salicylic acid

Under natural conditions plants have to cope with a wide range of abiotic and biotic stressors that occur simultaneously or in sequence, and phytohormones and reactive oxygen species are key mediators of plant stress response. However, their role in defence against abiotic and biotic stresses acting in combination still needs elucidation. We studied the involvement of reactive oxygen species, antioxidant enzymes, abscisic acid and salicylic acid in the response of cucumber plants exposed to individual or sequential action of salt stress (50mM or 100mM NaCl) and Pseudomonas syringae pv. lachrymans. Salt stress was more harmful than infection, especially with respect to leaf growth and stomata opening. The effects were most severe when the stresses were combined. Cucumber response to the pathogen infection was negatively affected by prior NaCl treatment. NaCl-induced changes promoted the pathogen growth and intensified the disease symptoms. It also provoked specific interactions between stress signalling components at the levels of hormones and the prooxidant/antioxidant mechanisms, exemplified by stronger H2O2 accumulation and Fe superoxide dismutase activation, changed salicylic acid/abscisic acid balance and modified PR1 gene expression.

Differential Responses in Germination, Growth and Genes Expression of Cu/Zn- and Fe-superoxide Dismutase of Barley Under Salinity Stress

Soil salinity limits crop productivity by affecting the growth, physiology, and expression of stress-responsive genes. To evaluate which varieties of cultivated barley from Jordan are salt tolerant, five cultivars of barley (Hordeum vulgare L.) of different varieties and morphotypes (i.e., two-and six-rowed barley) were evaluated in terms of their germination, growth traits, and gene expression of Cu/Zn- and Fe-SODs to three levels of salinity (100, 200 or 300 NaCl mM). Germination and root length were significantly affected by moderate and high levels of salinity (200 and 300 mM NaCl) mainly in the varieties Athroh, Mutah, Acsad176, Rum, and to lesser extent in Yarmouk variety, possibly as a consequence of osmotic stress and/or ionic toxicity. Analysis of quantitative real-time PCR (qRT-PCR) showed differential expressions of both Cu/Zn- and Fe-SOD genes between varieties and genotypes (i.e., the sixrowed barleys-Athroh, Acsad176, and Rum-and two-rowed barley-Yarmouk and Mutah). Moreover, both genes were up-regulated by salinity of 300 mM NaCl in the Athroh, Yarmouk, and Acsad176 varieties. Altogether, the result revealed that responses to salinity in all traits of germination, root growth, and gene expression were dependent on the variety and genotype of studied barley. Accordingly, these results have helped us to distinguish between salttolerant and salt-susceptible genotypes of cultivated barley of Jordan that shall be useful to local farmers and breeders of barley.

224 - Cytosolic Fe-Superoxide Dismutase Protects Trypanosoma Cruzi from Host-Derived Superoxide and Increases Pathogen Virulence in Vivo

Trypanosoma cruzi, the causative agent of Chagas Disease, contains Fe-dependent superoxide dismutases (Fe-SODs). After invasion, parasites have to deal with large amounts of superoxide radical (O2●–) produced during macrophage phagocytosis (NADPH-oxidase activation) and, in cytokine-activated macrophages (iNOS induction), with nitric oxide (●NO) and peroxynitrite. In this work, we studied the relevance of T. cruzi cytosolic Fe-SOD (Fe-SODB) during infection in vitro and in vivo. Fe-SODB-overexpressing parasites (TcFeSODB) were generated using the plasmid pRIBOTEX and expression evaluated by western-blot, immunocytochemistry and activity measurements. TcFeSODB parasites had less intra-parasite peroxynitrite generation than wt when exposed to O2●–- and ●NO fluxes, as evaluated by the oxidation of fluorescein boronate. They were also more resistant to macrophage killing (24hs after infection to J774A.1 or primary macrophages). These enhanced resistance, provided by high Fe-SOD levels in T. cruzi, was lost in NADPH-oxidase knockout macrophages (from gp91-/- mice). In the phagosome (pH ≈ 5-6), O2●–could be protonated (HO2●, pKa = 4,88) and diffuse towards parasite cytosol. This was confirmed by exposing the parasites to external fluxes of O2●– (generated by the system xanthine-oxidase/xanthine) at acidic and basic pHs (6 and 8 respectively). Intra-parasite 2-hydroxyethidium content (O2●–-specific product of dihydroethidium oxidation) was larger at pH=6 than pH=8. Additional entry mechanisms also participate, as the anion channel inhibitor NPPB, but not DIDS, decreased 2-hydroxyethidium detection. Inhibition of macrophage’s v-ATPase proton pump and prevention of phagosome acidification also decreases 2-hydroxyethidium detection in trypomastigotes 2h after infection. These results clearly show that O2●–can reach the parasite cytosol during phagocytosis. Finally, parasitemia in C57BL/6 infected mice (n=5) was larger (40%) for TcFeSODB than in wt parasites, demonstrating that Fe-SODB acts as a virulence factor in the mouse model of Chagas Disease.

PAH를 분해할 수 있는 Pseudomonas rhodesiae KK1의 SOD 유전자의 동정 및 분자학적 특성 분석

Pseudomonas rhodesiae KK1 has been reported to degrade polycyclic aromatic hydrocarbons (PAHs), such as anthracene, naphthalene, and phenanthrene, which are considered major environmental contaminants. Interestingly, antioxidant genes, including superoxide dismutase, are known to be expressed at different levels in response to environmental contaminants. This study was performed to identify the superoxide dismutase gene in strain KK1, which may be indirectly involved with degradation of PAHs, as well as to investigate the expression pattern of the superoxide dismutase gene in cells grown on different PAHs. Two types of superoxide dismutase genes responsible for the antioxidant defense mechanism, Mn-superoxide dismutase (sodA) and Fe-superoxide dismutase (sodB), were identified in P. rhodesiae KK1. The sodA gene in strain KK1 shared 95% similarity, based on 141 amino acids, with the Mn-sod of P. fluorescens Pf-5. The sodB strain, based on 135 amino acids, shared 99% similarity with the Fe-sod of P. fluorescens Pf-5. Southern hybridization using the sod gene fragment as a probe showed that at least two copies of superoxide dismutase genes exist in strain KK1. RT-PCR analysis revealed that the sodA and sodB genes were more strongly expressed in response to naphthalene and phenanthrene than to anthracene. Interestingly, sodA and sodB activities were revealed to be maintained in cells grown on all of the tested substrates, including glucose.

Entamoeba thiol-based redox metabolism: A potential target for drug development

Amebiasis is an intestinal infection widespread throughout the world caused by the human pathogen Entamoeba histolytica. Metronidazole has been a drug of choice against amebiasis for decades despite its low efficacy against asymptomatic cyst carriers and emergence of resistance in other protozoa with similar anaerobic metabolism. Therefore, identification and characterization of specific targets is urgently needed to design new therapeutics for improved treatment against amebiasis. Toward this goal, thiol-dependent redox metabolism is of particular interest. The thiol-dependent redox metabolism in E. histolytica consists of proteins including peroxiredoxin, rubrerythrin, Fe-superoxide dismutase, flavodiiron proteins, NADPH: flavin oxidoreductase, and amino acids including l-cysteine, S-methyl-l-cysteine, and thioprolines (thiazolidine-4-carboxylic acids). E. histolytica completely lacks glutathione and its metabolism, and l-cysteine is the major intracellular low molecular mass thiol. Moreover, this parasite possesses a functional thioredoxin system consisting of thioredoxin and thioredoxin reductase, which is a ubiquitous oxidoreductase system with antioxidant and redox regulatory roles. In this review, we summarize and highlight the thiol-based redox metabolism and its control mechanisms in E. histolytica, in particular, the features of the system unique to E. histolytica, and its potential use for drug development against amebiasis.

Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on <em>Arabidopsis thaliana </em>Development and Gene Expression

One of the most stimulating observations in plant evolution is a correlation between the occurrence of geomagnetic field (GMF) reversals (or excursions) and the moment of the radiation of Angiosperms. This led to the hypothesis that alterations in GMF polarity may play a role in plant evolution. Here, we describe a method to test this hypothesis by exposing Arabidopsis thaliana to artificially reversed GMF conditions. We used a three-axis magnetometer and the collected data were used to calculate the magnitude of the GMF. Three DC power supplies were connected to three Helmholtz coil pairs and were controlled by a computer to alter the GMF conditions. Plants grown in Petri plates were exposed to both normal and reversed GMF conditions. Sham exposure experiments were also performed. Exposed plants were photographed during the experiment and images were analyzed to calculate root length and leaf areas. Arabidopsis total RNA was extracted and Quantitative Real Time-PCR (qPCR) analyses were performed on gene expression of CRUCIFERIN 3 (CRU3), copper transport protein1 (COTP1), Redox Responsive Transcription Factor1 (RRTF1), Fe Superoxide Dismutase 1, (FSD1), Catalase3 (CAT3), Thylakoidal Ascorbate Peroxidase (TAPX), a cytosolic Ascorbate Peroxidase1 (APX1), and NADPH/respiratory burst oxidase protein D (RbohD). Four different reference genes were analysed to normalize the results of the qPCR. The best of the four genes was selected and the most stable gene for normalization was used. Our data show for the first time that reversing the GMF polarity using triaxial coils has significant effects on plant growth and gene expression. This supports the hypothesis that GMF reversal contributes to inducing changes in plant development that might justify a higher selective pressure, eventually leading to plant evolution.

Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on Arabidopsis thaliana Development and Gene Expression.

One of the most stimulating observations in plant evolution is a correlation between the occurrence of geomagnetic field (GMF) reversals (or excursions) and the moment of the radiation of Angiosperms. This led to the hypothesis that alterations in GMF polarity may play a role in plant evolution. Here, we describe a method to test this hypothesis by exposing Arabidopsis thaliana to artificially reversed GMF conditions. We used a three-axis magnetometer and the collected data were used to calculate the magnitude of the GMF. Three DC power supplies were connected to three Helmholtz coil pairs and were controlled by a computer to alter the GMF conditions. Plants grown in Petri plates were exposed to both normal and reversed GMF conditions. Sham exposure experiments were also performed. Exposed plants were photographed during the experiment and images were analyzed to calculate root length and leaf areas. Arabidopsis total RNA was extracted and Quantitative Real Time-PCR (qPCR) analyses were performed on gene expression of CRUCIFERIN 3 (CRU3), copper transport protein1 (COTP1), Redox Responsive Transcription Factor1 (RRTF1), Fe Superoxide Dismutase 1, (FSD1), Catalase3 (CAT3), Thylakoidal Ascorbate Peroxidase (TAPX), a cytosolic Ascorbate Peroxidase1 (APX1), and NADPH/respiratory burst oxidase protein D (RbohD). Four different reference genes were analysed to normalize the results of the qPCR. The best of the four genes was selected and the most stable gene for normalization was used. Our data show for the first time that reversing the GMF polarity using triaxial coils has significant effects on plant growth and gene expression. This supports the hypothesis that GMF reversal contributes to inducing changes in plant development that might justify a higher selective pressure, eventually leading to plant evolution.

Impact of the genetically engineered enhancement of the antioxidant protection of tobacco on the streptomycete complex in the rhizosphere of transformant plants

Tobacco (Nicotiana tabacum L.) plants with the gene of Fe-superoxide dismutase (Fe SOD1) from Arabidopsis thaliana L., which confers resistance to plants against the damaging effects of oxidative stress, have been used in the work. The abundances and structures of complexes of actinomycetes of the genus Streptomyces in the rhizosphere and rhizoplane of the original variety Samsun and independent transgenic lines Trtf 3 and Trtf 13 have been compared. The plants have been grown under optimum conditions (control) and on a native acidic soddy–podzolic soil under aluminum stress. The results show that the heterologous sequence inserted into the tobacco genome has a significant impact on the abundance, species diversity, and functional activity of streptomycetes in the rhizosphere of transformant plants.

Synthesis and evaluation of in vitro and in vivo trypanocidal properties of a new imidazole-containing nitrophthalazine derivative

A series of new phthalazine derivatives (1–4) containing imidazole rings and functionalized with nitro groups in the benzene ring of the phthalazine moiety were prepared and identified on the basis of their MS, elemental analyses and bidimensional 1H and 13C NMR data, and their trypanocidal activity was tested. The 8-nitrosubstituted compound (3) was more active in vitro against Trypanosoma cruzi and less toxic against Vero cells than the reference drug benznidazole, and showed a SI value that was 47-fold better than the reference drug in amastigote forms. It also remarkably reduced the infectivity rate in Vero cells and decreased the reactivation of parasitemia in immunodeficient mice. Ultrastructural alterations found in epimastigotes treated with 3 confirmed extensive cytoplasm destruction in the parasites, whereas histopathological analysis of the hearts of mice infected and treated with 3 resulted in a decrease in cardiac damage. Biochemical markers showed that livers, hearts, and kidneys of treated mice were substantially unaffected by the administration of 3, despite the presence of the potentially toxic nitro group. It was also found that this compound selectively inhibited the antioxidant parasite enzyme Fe–superoxide dismutase (Fe–SOD) in comparison with human CuZn–SOD, and molecular modeling suggested interaction with the H-bonding system of the iron-based moiety as a feasible mechanism of action against the enzyme.

CONSTRUCTING AND STUDYING OF THE PROPERTIES OF Francisella tularensis 15 NIIEG VARIANTS WITH REDUCED EXPRESSION OF sodB GENE ENCODING Fe-SUPEROXIDE DISMUTASE

Within the frames of the investigation on constructing of an improved live tularemia vaccine with less reactogenicity by the method of allelic replacement using a suicidal plasmid pGM5, the mutant variants have been obtained from the vaccine strain Francisella tularensis 15 NIIEG with a reduced expression of the superoxide dismutase sodB gene. This reduction was a result of the substitution of rare for frequent natural codons in the F e-superoxide dismutase (FeSOD) gene. It was shown that the decrease in the FeSOD production up to 30% of the level in the original strain had no negative effect on the rate of the tularemia cause reproduction. It was shown that the mutant strains were more sensitive to hydrogen peroxide and paraquat as compared to the vacci- he bacteria. All the strains were shown (by Q-PCR) to have at the log phase the elevated content of gene groEL mRNA encoding GroEL chaperone.

Formation of high-order oligomers by a hyperthemostable Fe-superoxide dismutase (tcSOD).

Hyperthermostable proteins are highly resistant to various extreme conditions. Many factors have been proposed to contribute to their ultrahigh structural stability. Some thermostable proteins have larger oligomeric size when compared to their mesophilic homologues. The formation of compact oligomers can minimize the solvent accessible surface area and increase the changes of Gibbs free energy for unfolding. Similar to mesophilic proteins, hyperthermostable proteins also face the problem of unproductive aggregation. In this research, we investigated the role of high-order oligomerization in the fight against aggregation by a hyperthermostable superoxide dismutase identified from Tengchong, China (tcSOD). Besides the predominant tetramers, tcSOD could also form active high-order oligomers containing at least eight subunits. The dynamic equilibrium between tetramers and high-order oligomers was not significantly affected by pH, salt concentration or moderate temperature. The secondary and tertiary structures of tcSOD remained unchanged during heating, while cross-linking experiments showed that there were conformational changes or structural fluctuations at high temperatures. Mutational analysis indicated that the last helix at the C-terminus was involved in the formation of high-order oligomers, probably via domain swapping. Based on these results, we proposed that the reversible conversion between the active tetramers and high-order oligomers might provide a buffering system for tcSOD to fight against the irreversible protein aggregation pathway. The formation of active high-order oligomers not only increases the energy barrier between the native state and unfolded/aggregated state, but also provides the enzyme the ability to reproduce the predominant oligomers from the active high-order oligomers.

Isolation and in silico analysis of Fe-superoxide dismutase in the cyanobacterium Nostoc commune

Cyanobacteria are known to endure various stress conditions due to the inbuilt potential for oxidative stress alleviation owing to the presence of an array of antioxidants. The present study shows that Antarctic cyanobacterium Nostoc commune possesses two antioxidative enzymes viz., superoxide dismutase (SOD) and catalase that jointly cope with environmental stresses prevailing at its natural habitat. Native-PAGE analysis illustrates the presence of a single prominent isoform recognized as Fe-SOD and three distinct isoforms of catalase. The protein sequence of Fe-SOD in N. commune retrieved from NCBI protein sequence database was used for in silico analysis. 3D structure of N. commune was predicted by comparative modeling using MODELLER 9v11. Further, this model was validated for its quality by Ramachandran plot, ERRAT, Verify 3D and ProSA-web which revealed good structure quality of the model. Multiple sequence alignment showed high conservation in N and C-terminal domain regions along with all metal binding positions in Fe-SOD which were also found to be highly conserved in all 28 cyanobacterial species under study, including N. commune. In silico prediction of isoelectric point and molecular weight of Fe-SOD was found to be 5.48 and 22,342.98Da respectively. The phylogenetic tree revealed that among 28 cyanobacterial species, Fe-SOD in N. commune was the closest evolutionary homolog of Fe-SOD in Nostoc punctiforme as evident by strong bootstrap value. Thus, N. commune may serve as a good biological model for studies related to survival of life under extreme conditions prevailing at the Antarctic region. Moreover cyanobacteria may be exploited for biochemical and biotechnological applications of enzymatic antioxidants.

Pb-induced responses in Zygophyllum fabago plants are organ-dependent and modulated by salicylic acid

Zygophyllum fabago is a promising species for restoring heavy metal (HM) polluted soils, although the mechanisms involved in HM tolerance in this non-model plant remain largely unknown. This paper analyses the extent to which redox-active compounds and enzymatic antioxidants in roots, stems and leaves are responsible for Pb tolerance in a metallicolous ecotype of Z. fabago and the possible influence of salicylic acid (SA) pretreatment (24 h, 0.5 mM SA) in the response to Pb stress. SA pretreatment reduced both the accumulation of Pb in roots and even more so the concentration of Pb in aerial parts of the plants, although a similar drop in the content of chlorophylls and in the maximum quantum yield of photosystem II was observed in both Pb- and SA-Pb-treated plants. Pb increased the endogenous free SA levels in all organs and this response was enhanced in root tissues upon SA pretreatment. Generally, Pb induced a reduction in catalase, ascorbate peroxidase and glutathione reductase specific activities, whereas dehydroascorbate reductase was increased in all organs of control plants. SA pretreatment enhanced the Pb-induced H2O2 accumulation in roots by up-regulating Fe-superoxide dismutase isoenzymes. Under Pb stress, the GSH redox ratio remained highly reduced in all organs while the ascorbic acid redox ratio dropped in leaf tissues where a rise in lipid peroxidation products and electrolyte leakage was observed. Finally, an organ-dependent accumulation of proline and β-carboline alkaloids was found, suggesting these nitrogen-redox-active compounds could play a role in the adaptation strategies of this species to Pb stress.

Evaluation of the anti-nitrative effect of plant antioxidants using a cowpea Fe-superoxide dismutase as a target

Nitric oxide cytotoxicity arises from its rapid conversion to peroxynitrite (ONOO−) in the presence of superoxide, provoking functional changes in proteins by nitration of tyrosine residues. The physiological significance of this post-translational modification is associated to tissue injury in animals, but has not been yet clarified in plants. The objective of this study was to establish new approaches that could help to understand ONOO− reactivity in plants. A recombinant Fe-superoxide dismutase from cowpea (Vigna unguiculata (L.) Walp.), rVuFeSOD, was the target of the ONOO−-generator SIN-1, and the anti-nitrative effect of plant antioxidants and haemoglobins was tested in vitro. Nitration on rVuFeSOD was evaluated immunochemically or as the loss of its enzymatic activity. This assay proved to be useful to test a variety of plant compounds for anti-nitrative capacity. Experimental data confirmed that rice (Oryza sativa L.) haemoglobin-1 (rOsHbI) and cowpea leghaemoglobin-2 exerted a protective function against ONOO− by diminishing nitration on rVuFeSOD. Both plant haemoglobins were nitrated by SIN-1. The chelator desferrioxamine suppressed nitration in rOsHbI, indicating that Fe plays a key role in the reaction. The removal of the haem moiety in rOsHbI importantly suppressed nitration, evidencing that this reaction may be self-catalyzed. Among small antioxidants, ascorbate remarkably decreased nitration in all tests. The phenolic compounds caffeic acid, gallic acid, pyrogallol, 4-hydroxybenzoic acid and the flavonoid gossypin also diminished tyrosine nitration and protected rVuFeSOD to different extents. It is concluded that small plant antioxidants, especially ascorbate, and haemoglobins may well play key roles in ONOO− homeostasis in vivo.

Unravelling the cross-talk between iron starvation and oxidative stress responses highlights the key role of PerR (alr0957) in peroxide signalling in the cyanobacterium Nostoc PCC 7120.

The cyanobacterial phylum includes oxygenic photosynthetic prokaryotes of a wide variety of morphologies, metabolisms and ecologies. Their adaptation to their various ecological niches is mainly achieved by sophisticated regulatory mechanisms and depends on a fine cross-talk between them. We assessed the global transcriptomic response of the filamentous cyanobacterium Nostoc PCC 7120 to iron starvation and oxidative stress. More than 20% of the differentially expressed genes in response to iron stress were also responsive to oxidative stress. These transcripts include antioxidant proteins-encoding genes that confirms that iron depletion leads to reactive oxygen accumulation. The activity of the Fe-superoxide dismutase was not significantly decreased under iron starvation, indicating that the oxidative stress generated under iron deficiency is not a consequence of (SOD) deficiency. The transcriptional data indicate that the adaptation of Nostoc to iron-depleted conditions displays important differences with what has been shown in unicellular cyanobacteria. While the FurA protein that regulates the response to iron deprivation has been well characterized in Nostoc, the regulators in charge of the oxidative stress response are unknown. Our study indicates that the alr0957 (perR) gene encodes the master regulator of the peroxide stress. PerR is a peroxide-sensor repressor that senses peroxide by metal-catalysed oxidation.

Differential responses of antioxidant enzymes to aluminum toxicity in two rice (Oryza sativa L.) cultivars with marked presence and elevated activity of Fe SOD and enhanced activities of Mn SOD and catalase in aluminum tolerant cultivar

Seedlings of two Indica rice (Oryza sativa L.) cvs. HUR-105 and Vandana, differing in Al-tolerance were used to identify the key mechanisms involved in their differential behaviour towards Al toxicity. Cv. HUR-105 appeared to be Al sensitive by showing significant reduction (p ≤ 0.01) in root/shoot length, fresh weight, dry weight and water content in presence of 421 μM Al3+ in growth medium whereas cv. Vandana appeared to be fairly Al3+ tolerant. A conspicuous and significant reduction in dry weight of root and shoot was observed in Al sensitive cv. HUR-105 with 178 μM Al3+ treatment for 3 days. Al was readily taken up by the roots and transported to shoots in both the rice cultivars. Localization of absorbed Al was always greater in roots than in shoots. Our results of the production of reactive oxygen species (ROS) H2O2 and O2.− and activities of major antioxidant enzymes such as total superoxide dismutase (SOD), Cu/Zn SOD, Mn SOD, Fe SOD, catalase (CAT) and guaiacol peroxidase revealed Al induced higher oxidative stress, greater production of ROS and lesser capacity to scavenge ROS in cv. HUR-105 than Vandana. With Al treatment, higher oxidative stress was noted in shoots than in roots. Greatly enhanced activities of SOD (especially Fe and Mn SOD) and CAT in Al treated seedlings of cv. Vandana suggest the role of these enzymes in Al tolerance. Furthermore, a marked presence of Fe SOD in roots and shoots of the seedlings of Al tolerant cv. Vandana and its significant (p ≤ 0.01) increase in activity due to Al-treatment, appears to be the unique feature of this cultivar and indicates a vital role of Fe SOD in Al-tolerance in rice.

Modeling and analysis of soybean (Glycine max. L) Cu/Zn, Mn and Fe superoxide dismutases

Superoxide dismutase (SOD, EC 1.15.1.1) is an important metal-containing antioxidant enzyme that provides the first line of defense against toxic superoxide radicals by catalyzing their dismutation to oxygen and hydrogen peroxide. SOD is classified into four metalloprotein isoforms, namely, Cu/Zn SOD, Mn SOD, Ni SOD and Fe SOD. The structural models of soybean SOD isoforms have not yet been solved. In this study, we describe structural models for soybean Cu/Zn SOD, Mn SOD and Fe SOD and provide insights into the molecular function of this metal-binding enzyme in improving tolerance to oxidative stress in plants.