Descripción: A scheme for resolving average optical rotatory power of a molecule into atomic contributions, applied to hydrogen peroxide, is presented. The scheme is based on the acceleration gauge for the electric dipole, and the torque formalism. Calculations are carried out to test the reliability of the partition method. The force and torque gauges provide different numerical values for atomic contributions.

Descripción: MAP kinases have been linked to guard cell signalling. Arabidopsis thaliana MAP Kinase 3 (MPK3) is known to be activated by abscisic acid (ABA) and hydrogen peroxide (H2O2), which also control stomatal movements. We therefore studied the possible role of MPK3 in guard cell signalling through guard cell-specific antisense inhibition of MPK3 expression. Such transgenic plants contained reduced levels of MPK3 mRNA in the guard cells and displayed partial insensitivity to ABA in inhibition of stomatal opening, but responded normally to this hormone in stomatal closure. However, ABA-induced stomatal closure was reduced compared with controls when cytoplasmic alkalinization was prevented with sodium butyrate. MPK3 antisense plants were less sensitive to exogenous H2O2, both in inhibition of stomatal opening and in promotion of stomatal closure, thus MPK3 is required for the signalling of this compound. ABA-induced H2O2 synthesis was normal in these plants, indicating that MPK3 probably acts in signalling downstream of H2O2. These results provide clear evidence for the important role of MPK3 in the perception of ABA and H 2O2 in guard cells. © The Authors (2007).

Descripción: We applied a methodology capable of resolving the optical rotatory power into atomic contributions. The individual atomic contributions to the optical rotatory power and molecular chirality of the methylhydroperoxide are obtained via a canonical transformation of the Hamiltonian by which the electric dipolar moment operator is transformed to the acceleration gauge formalism and the magnetic dipolar moment operator to the torque formalism. The gross atomic isotropic contributions have been evaluated for the carbon, the nonequivalent oxygen, and the nonequivalent hydrogen atoms of methylhydroperoxide, employing a very large Gaussian basis set which is close to the Hartree-Fock limit. © 2008 American Institute of Physics.

Descripción: Exposure of either gametes or embryos to conditions and/or factors that generate oxidative stress has been associated with impaired early embryogenesis. The effects of reactive oxygen species (ROS) on mouse preimplantation development, depending of the ROS-concentration and time of exposition, were studied. Two-cell embryos were incubated with 5, 10, 25 and 50 μM of hydrogen peroxide (H2O2) for 30 and 60 minutes of exposition and allowed to develop for 72 h to study the quality of development. The incubation with 50 μM H2O2 for 30 or 60 minutes, strongly inhibited the 2-cell embryo development as compared to the control (p<0.001). Twenty-five μM H2O2 produced inhibition of blastocyst formation (p<0.001) and 10 μM H2O2 significantly decreased the percentages of expanded and hatched blastocysts, which resulted morphologically altered (p<0.05 and p<0.01, respectively). The higher H2O2 concentrations were able to elicit necrotic morphology in the 2-cell arrested embryos, while 10 μM H2O 2 induced moderate damage with the arrested embryos partially fragmented. In conclusion, important causes for defective preimplantation development and for early embryo losses may be due to oxidative stress because early mouse embryos exposed to ROS for short times arrested at the first cellular cycle (2-cell) and/or impaired embryo differentiation and morphogenesis, being these effects ROS-concentration-dependent.

Descripción: The effect of pore size to H2O2 detection by macroporous and mesoporous Prussian blue type electrocatalysts is reported in the present paper. The macroporous electrocatalysts were prepared employing spherical colloidal particles of different sizes (300, 460, 600 and 800 nm) as sacrificial templates to synthesize a copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) hybrid material. Surprisingly, macroporous and non-porous CuHCNFe/Ppy displayed very similar results, which led to a discussion that application of macroporous platforms in sensors must consider the material wettability and the influence of electrochemical kinetics on analyte detection. In order to evaluate the effect of smaller pores, the performance of the macroporous H2O2 sensors was also compared to electrocatalysts synthesised through the immobilization of Prussian blue and CuHCNFe layers inside the cavities of mesoporous TiO2 films with diameters of 13, 20 and 40 nm. In this scale, the results were superior than those achieved with the non-porous sensors, demonstrating the possibility of controlling the performance of H2O2 sensors according to the pore diameter and the amount of immobilized material. Among the tested porous materials, the H2O2 sensor with better performance was achieved using the 20-nm diameter TiO2 platform functionalized with Prussian blue, which presented a sensitivity of (930 ± 50) μA cm-2 mmol-1 L, detection limit of (0.49 ± 0.08) μmol L-1, response time of (6 ± 2) seconds and linear range up to (1.3 ± 0.1) mmol L-1. This performance was extremely satisfactory considering sensors operating by chronoamperometry. © 2013 Elsevier Ltd. All rights reserved.

Descripción: 2-Cys peroxiredoxins (2-Cys Prxs) are ubiquitous peroxidases with important roles in cellular antioxidant defense and hydrogen peroxide-mediated signaling. Post-translational modifications of conserved cysteines cause the transition from low to high molecular weight oligomers, triggering the functional change from peroxidase to molecular chaperone. However, it remains unclear how non-covalent interactions of 2-Cys Prx with metabolites modulate the quaternary structure. Here, we disclose that ATP and Mg2+ (ATP/Mg) promote the self-polymerization of chloroplast 2-Cys Prx (polypeptide 23.5 kDa) into soluble higher order assemblies (>2 MDa) that proceed to insoluble aggregates beyond 5mMATP. Remarkably, the withdrawal of ATP or Mg2+ brings soluble oligomers and insoluble aggregates back to the native conformation without compromising the associated functions. As confirmed by transmission electron microscopy, ATP/Mg drive the toroid-like decamers (diameter 13 nm) to the formation of large sphere-like particles (diameter ∼30 nm). Circular dichroism studies on ATP-labeled 2-Cys Prx reveal that ATP/Mg enhance the proportion of β-sheets with the concurrent decrease in the content of α-helices. In line with this observation, the formation of insoluble aggregates is strongly prevented by 2,2,2-trifluoroethanol, a cosolvent employed to induce α-helical conformations. We further find that the response of self-polymerization to ATP/Mg departs abruptly from that of the associated peroxidase and chaperone activities when two highly conserved residues, Arg129 and Arg152, are mutated. Collectively, our data uncover that non-covalent interactions of ATP/Mg with 2-Cys Prx modulate dynamically the quaternary structure, thereby coupling the non-redox chemistry of cell energy with redox transformations at cysteine residues. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: To determine whether the stationary sigma factor, σS, influences polyhydroxyalkanoate metabolism in Pseudomonas putida KT2440, an rpoS-negative mutant was constructed to evaluate polyhydroxyalkanoate accumulation and expression of a translational fusion to the promoter region of the genes that code for polyhydroxyalkanoate synthase 1 (phaC1) and polyhydroxyalkanoate depolymerase (phaZ). By comparison with the wild-type, the rpoS mutant showed a higher polyhydroxyalkanoate degradation rate and increased expression of the translational fusion during the stationary growth phase. These results suggest that σS might control the genes involved in polyhydroxyalkanoate metabolism, possibly in an indirect manner. In addition, survival and oxidative stress assays performed under polyhydroxyalkanoate- and nonpolyhydroxyalkanoate- accumulating conditions demonstrated that the accumulated polyhydroxyalkanoate increased the survival and stress tolerance of the rpoS mutant. According to this, polyhydroxyalkanoate accumulation would help cells to overcome the adverse conditions encountered during the stationary phase in the strain that lacks RpoS. © 2008 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.