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Crushed stone waste produced by the stone crushing in the production of aggregate for the construction industry is currently discharged in large stockpiles that facilitate the dispersion of the particles by wind currents and rainwater. Such dispersion leads to environmental issues due to suspended particles in the air and natural bodies of water, as well as dust deposited on vegetation, soil, and urban settlements neighboring the quarry. To upgrade these solids to the status of feedstock for the synthesis of materials, this work developed a conversion process for the crushed stone waste into pure zeolites Na-A, Na-X, and analcime. The high concentration of silicon in this waste encouraged this application. Mild synthesis conditions were established from the analysis of the effect of the SiO 2 /Al 2 O 3 mass ratio and the crystallization temperature and time on the type of produced zeolite. Zeolites Na-X showed BET surface areas between 552 and 620 m2/g. Pb2+ and Cd2+ removal from aqueous solutions by zeolites Na-A and Na-X was investigated at different pHs through adsorption isotherms. The adsorption capacities were 555.6 and 454.5 mg Pb2+/g zeolite for zeolites Na-A and Na-X, respectively. 158.7 and 113.6 mg Cd2+/g zeolite were the corresponding capacities in the case of Cd2+. [Display omitted] • Chemical process for the conversion of crushed stone fines into pure zeolites. • Crushed stone waste upgraded to the status of feedstock for chemical processes. • Mild crystallization conditions for zeolites Na-X, Na-A, and analcime. • Langmuir adsorption model fitting for Pb2+ and Cd2+ adsorption in aqueous solutions. • Zeolites with high adsorption capacities for Pb2+ and Cd2+ in aqueous solutions. [ABSTRACT FROM AUTHOR]

Systematic changes in interfacial forces, turbulence models for the continuous and dispersed phases, lift force coefficient, and bubble size distribution were used to evaluate, in terms of complexity, the performance of nine computational models in the simulation of the time-averaged axial liquid velocity and holdup profiles in a bubble column. The oscillation period of the gas plume was also included in this evaluation. The mesh used for the simulations was chosen after a convergence analysis carried out with four meshes. The finest mesh displayed the highest divergence from the experimental data. Such behavior indicates that the proper mesh for a simulation of a multiphase flow must consider other factors in addition to element size and the quality indicators. The standard, RNG, and realizable κ-ε models were used for the liquid phase, while an algebraic and the standard κ-ε were the models for the dispersed phase. The isotropic RNG model for the liquid phase achieved accurate predictions in the anisotropic region near the gas distributor. The algebraic approach for the gas phase produced data similar to those calculated with the standard model. The simultaneous presence of the lift and virtual mass forces led to reliable predictions, and a lift coefficient of 0.2 displayed better performance than 0.14. This coefficient produced an excessive dampening of the lift force and caused the simulations to lose accuracy. The population balances did not improve the predictions. [Display omitted] • Systematic assessment of computational models for simulations of bubble columns. • Significant role of the lift and virtual mass forces in the quality of simulations. • The lift force is part of the mechanisms producing the oscillation of the gas plume. • Additional factors to the grid convergence for choosing the right mesh. • Algebraic model of the dispersed phase simplifies the simulations. [ABSTRACT FROM AUTHOR]

Mycobacterium tuberculosis (M. tuberculosis), the pathogen responsible for tuberculosis, detoxifies cytotoxic peroxides produced by activated macrophages. M. tuberculosis expresses alkyl hydroxyperoxide reductase E (AhpE), among other peroxiredoxins. So far the system that reduces AhpE was not known. We identified M. tuberculosis mycoredoxin-1 (MtMrx1) acting in combination with mycothiol and mycothiol disulfide reductase (MR), as a biologically relevant reducing system for MtAhpE. MtMrx1, a glutaredoxin-like, mycothiol-dependent oxidoreductase, directly reduces the oxidized form of MtAhpE, through a protein mixed disulfide with the N-terminal cysteine of MtMrx1 and the sulfenic acid derivative of the peroxidatic cysteine of MtAhpE. This disulfide is then reduced by the C-terminal cysteine in MtMrx1. Accordingly, MtAhpE catalyzes the oxidation of wt MtMrx1 by hydrogen peroxide but not of MtMrx1 lacking the C-terminal cysteine, confirming a dithiolic mechanism. Alternatively, oxidized MtAhpE forms a mixed disulfide with mycothiol, which in turn is reduced by MtMrx1 using a monothiolic mechanism. We demonstrated the H2O2-dependent NADPH oxidation catalyzed by MtAhpE in the presence of MR, Mrx1, and mycothiol. Disulfide formation involving mycothiol probably competes with the direct reduction by MtMrx1 in aqueous intracellular media, where mycothiol is present at millimolar concentrations. However, MtAhpE was found to be associated with the membrane fraction, and since mycothiol is hydrophilic, direct reduction by MtMrx1 might be favored. The results reported herein allow the rationalization of peroxide detoxification actions inferred for mycothiol, and more recently, for Mrx1 in cellular systems. We report the first molecular link between a thiol-dependent peroxidase and the mycothiol/Mrx1 pathway in Mycobacteria. [ABSTRACT FROM AUTHOR]

Abstract: Alkyl hydroperoxide reductase E (AhpE), a novel subgroup of the peroxiredoxin family, comprises Mycobacterium tuberculosis AhpE (MtAhpE) and AhpE-like proteins present in many bacteria and archaea, for which functional characterization is scarce. We previously reported that MtAhpE reacted ~103 times faster with peroxynitrite than with hydrogen peroxide, but the molecular reasons for that remained unknown. Herein, we investigated the oxidizing substrate specificity and the oxidative inactivation of the enzyme. In most cases, both peroxidatic thiol oxidation and sulfenic acid overoxidation followed a trend in which those peroxides with the lower leaving-group pK a reacted faster than others. These data are in agreement with the accepted mechanisms of thiol oxidation and support that overoxidation occurs through sulfenate anion reaction with the protonated peroxide. However, MtAhpE oxidation and overoxidation by fatty acid-derived hydroperoxides (~108 and 105 M−1 s−1, respectively, at pH 7.4 and 25°C) were much faster than expected according to the Brønsted relationship with leaving-group pK a. A stoichiometric reduction of the arachidonic acid hydroperoxide 15-HpETE to its corresponding alcohol was confirmed. Interactions of fatty acid hydroperoxides with a hydrophobic groove present on the reduced MtAhpE surface could be the basis of their surprisingly fast reactivity. [Copyright &y& Elsevier]

Abstract: Empirical airborne remote-sensing relationships were examined to estimate chlorophyll a concentration in the first optical depth (chlFOD) of coastal waters of Afgonak/Kodiak Islands during July–August 2002. Band-ratio and spectral-curvature models were tested using satellite remote-sensing reflectance (R rs(λ)) measurements. Additional shipboard and airborne R rs(λ) data were also analysed to evaluate consistency of proposed chlFOD–R rs(λ) relationships. Validation of chlorophyll algorithms was performed using data collected in the northern-part of the Gulf of Alaska and Bering Sea during 1996, 2002, and 2003 cruises. Likewise, oceanographic conditions during the surveys were typified to interpret variability of chlFOD fields. The SeaWiFS band-ratio algorithm OC2d was the most sensitive R rs combination (R rs(509)/R rs(553)) to detect chlFOD variability. Conversely, OC2a (R rs(412)/R rs(553)) had the lowest performance to derive chlFOD values. No valid statistical regressions were established for spectral–curvature relationships in the blue spectrum (<500 nm). Fertile waters (>5 mg m−3) were preferentially located over shallow banks (∼50 m) and at the entrance of the bays. The approach used in this study to derive chlFOD values could be universal for Alaskan coastal waters. However, chlFOD–R rs(λ) relationships must be calibrated locally for a given season. [Copyright &y& Elsevier]

The main machinery responsible for cellular protein maintenance is the ubiquitin-proteasomal system. The main task of the system is a fast and efficient degradation of proteins not needed anymore in cellular metabolism. It is accepted that upon oxidative stress, the proteasome suffers a series of functional alterations, including a reversible, oxidation-triggered 26 S proteasome disassembly into its catalytic (CP) and regulatory (RP) particles. Formation of low fluxes of oxidants were stimulated with antimycin or palmitic acid in pancreatic MIN6 cells, inducing a partial increase of dimerization of mitochondrial and citosolic peroxiredoxins. Under this conditions, no significant increase of total protein thiol oxidation was detected. However, ATP-stimulation of 26 S proteasomes was inhibited while the particle remained fully assemblied. Discrete cysteine residues of both CP and RP were identified oxidized by a cysteine-targeted proteomics approach. Such results may rely on differential reactivity of cysteines in the subunits and suggest specific regulation of particles by discrete cysteine oxidation. Further studies will elucidate the type of modification on each cysteine residue and the impact. Our results suggest a novel mechanism of redox regulation of 26 S proteasome that precedes oxidation-driven 26 S particle disassembly. [ABSTRACT FROM AUTHOR]

Methylglyoxal (MG), a highly reactive dicarbonyl, interacts with proteins to form advanced glycation end products (AGEs). AGEs include a variety of compounds which were shown to have damaging potential and to accumulate in the course of different conditions such as diabetes mellitus and aging. After confirming collagen as a main target for MG modifications in vivo within the extracellular matrix, we show here that MG-collagen disrupts fibroblast redox homeostasis and induces endoplasmic reticulum (ER) stress and apoptosis. In particular, MG-collagen-induced apoptosis is associated with the activation of the PERK-eIF2α pathway and caspase-12. MG-collagen contributes to altered redox homeostasis by directly generating hydrogen peroxide and oxygen-derived free radicals. The induction of ER stress in human fibroblasts was confirmed using collagen extracts isolated from old mice in which MG-derived AGEs were enriched. In conclusion, MG-derived AGEs represent one factor contributing to diminished fibroblast function during aging. [ABSTRACT FROM AUTHOR]

Peroxiredoxins (Prx) are efficient thiol-dependent peroxidases and key players in the mechanism of H2O2-induced redox signaling. Any structural change that could affect their redox state, oligomeric structure, and/or interaction with other proteins could have a significant impact on the cascade of signaling events. Several post-translational modifications have been reported to modulate Prx activity. One of these, overoxidation of the peroxidatic cysteine to the sulfinic derivative, inactivates the enzyme and has been proposed as a mechanism of H2O2 accumulation in redox signaling (the floodgate hypothesis). Nitration of Prx has been reported in vitro as well as in vivo; in particular, nitrated Prx2 was identified in brains of Alzheimer disease patients. In this work we characterize Prx2 tyrosine nitration, a post-translational modification on a noncatalytic residue that increases its peroxidase activity and its resistance to overoxidation. Mass spectrometry analysis revealed that treatment of disulfide-oxidized Prx2 with excess peroxynitrite renders mainly mononitrated and dinitrated species. Tyrosine 193 of the YF motif at the C terminus, associated with the susceptibility toward overoxidation of eukaryotic Prx, was identified as nitrated and is most likely responsible for the protection of the peroxidatic cysteine against oxidative inactivation. Kinetic analyses suggest that tyrosine nitration facilitates the intermolecular disulfide formation, transforming a sensitive Prx into a robust one. Thus, tyrosine nitration appears as another mechanism to modulate these enzymes in the complex network of redox signaling. [ABSTRACT FROM AUTHOR]

The white adipose tissue (WAT) is crucial for maintaining metabolism homeostasis by storing lipids and/or by secreting adipokines. A healthy WAT relies on continuous renewal, through a multi-step process called adipogenesis. Upon failure, the risk for lipotoxicity across the organism is higher and insulin resistance can arise in several tissues. A likely contributor for adipogenesis failure is mitochondrial dysfunction and subsequently cellular redox changes. Using 3T3-L1 cells, we have found that exposing them to hyperoxia (as a source of oxidative stress) for 8 days led to adipogenesis impairment, confirmed by oil red staining and transcription factors qPCRs. In our model, oxidative stressed preadipocytes exhibited mitochondrial dynamics diminishment (live cell imaging), Reactive Oxygen Species (ROS) production (fluorescence probe), less mitochondrial mass (WB and qPCR), smaller ATP/ADP ratio (HPLC) and less respiration capacity (Seahorse). In fact, challenging cells with antimycin, under normoxic conditions, showed similar features to hyperoxic treated cells in what adipogenesis is concerned. Recently, we found NFkB to be activated during the 8 days of hyperoxia in contrast to NFkB levels of differentiating cells which decreased after 2 days. We are convinced that mitochondrial dysfunction during aging/oxidative stress activates NFkB, blocking the main transcription factors and impairing adipogenesis. [ABSTRACT FROM AUTHOR]

Mycobacterium tuberculosis ( M. tuberculosis ) is the intracellular bacterium responsible for tuberculosis disease (TD). Inside the phagosomes of activated macrophages, M. tuberculosis is exposed to cytotoxic hydroperoxides such as hydrogen peroxide, fatty acid hydroperoxides and peroxynitrite. Thus, the characterization of the bacterial antioxidant systems could facilitate novel drug developments. In this work, we characterized the product of the gene Rv1608c from M. tuberculosis, which according to sequence homology had been annotated as a putative peroxiredoxin of the peroxiredoxin Q subfamily (PrxQ B from M. tuberculosis or Mt PrxQ B). The protein has been reported to be essential for M. tuberculosis growth in cholesterol-rich medium. We demonstrated the M. tuberculosis thioredoxin B/C-dependent peroxidase activity of Mt PrxQ B, which acted as a two-cysteine peroxiredoxin that could function, although less efficiently, using a one-cysteine mechanism. Through steady-state and competition kinetic analysis, we proved that the net forward rate constant of Mt PrxQ B reaction was 3 orders of magnitude faster for fatty acid hydroperoxides than for hydrogen peroxide (3×10 6 vs 6×10 3 M − 1 s − 1 , respectively), while the rate constant of peroxynitrite reduction was (0.6−1.4) ×10 6 M − 1 s − 1 at pH 7.4. The enzyme lacked activity towards cholesterol hydroperoxides solubilized in sodium deoxycholate. Both thioredoxin B and C rapidly reduced the oxidized form of Mt PrxQ B, with rates constants of 0.5×10 6 and 1×10 6 M − 1 s − 1 , respectively. Our data indicated that Mt PrxQ B is monomeric in solution both under reduced and oxidized states. In spite of the similar hydrodynamic behavior the reduced and oxidized forms of the protein showed important structural differences that were reflected in the protein circular dichroism spectra. [ABSTRACT FROM AUTHOR]

Trypanosoma cruzi, the causative agent of Chagas disease, contains exclusively iron-dependent superoxide dismutases (Fe-SODs) located in different subcellular compartments. Peroxynitrite, a key cytotoxic and oxidizing effector biomolecule, reacted with T. cruzi mitochondrial (Fe-SODA) and cytosolic (Fe-SODB) SODs with second order rate constants of 4.6 ± 0.2 x 104 M-1 s-1 and 4.3 ± 0.4 x 104 M-1 s-1 at pH 7.4 and 37 °C, respectively. Both isoforms are dose-dependently nitrated and inactivated by peroxynitrite. Susceptibility of T. cruzi Fe-SODA toward peroxynitrite was similar to that reported previously for Escherichia coli Mn- and Fe-SODs and mammalian Mn-SOD, whereas Fe-SODB was exceptionally resistant to oxidant-mediated inactivation. We report mass spectrometry analysis indicating that peroxynitrite-mediated inactivation of T. cruzi Fe-SODs is due to the site-specific nitration of the critical and universally conserved Tyr35. Searching for structural differences, the crystal structure of Fe-SODA was solved at 2.2 Å resolution. Structural analysis comparing both Fe-SOD isoforms reveals differences in key cysteines and tryptophan residues. Thiol alkylation of Fe-SODB cysteines made the enzyme more susceptible to peroxynitrite. In particular, Cys83 mutation (C83S, absent in Fe-SODA) increased the Fe-SODB sensitivity toward peroxynitrite. Molecular dynamics, electron paramagnetic resonance, and immunospin trapping analysis revealed that Cys83 present in Fe-SODB acts as an electron donor that repairs Tyr35 radical via intramolecular electron transfer, preventing peroxynitrite-dependent nitration and consequent inactivation of Fe-SODB. Parasites exposed to exogenous or endogenous sources of peroxynitrite resulted in nitration and inactivation of Fe-SODA but not Fe-SODB, suggesting that these enzymes play distinctive biological roles during parasite infection of mammalian cells. [ABSTRACT FROM AUTHOR]