Formation of Hydroxyl Radicals in Biological Systems. Does Myoglobin Stimulate Hydroxyl Radical Formation from Hydrogen Peroxide?

Incubation of horse-heart oxymyoglobin or metmyoglobin with excess H₂O₂ causes formation of myoglobin(IV), followed by haem degradation. At the time when haem degradation is observed, hydroxyl radicals (.OH) can be detected in the reaction mixture by their ability to degrade the sugar deoxyribose. Detection of hydroxyl radicals can be decreased by transferrin or by OH scavengers (mannitol, arginine, phenylalanine) but not by urea. Neither transferrin nor any of these scavengers inhibit the haem degradation. It is concluded that intact oxymyoglobin or metmyoglobin molecules do not react with H₂O₂ to form OH detectable by deoxyribose, but that H₂O₂ eventually leads to release of iron ions from the proteins. These released iron ions can react to form OH outside the protein or close to its surface. Salicylate and the iron chelator desferrioxamine stabilize myoglobin and prevent haem degradation. The biological importance of OH generated using iron ions released from myoglobin by H₂O₂ is discussed in relation to myocardial reoxygenation injury.     

A physiological and molecular study of the effects of nickel deficiency and phenylphosphorodiamidate (PPD) application on urea metabolism in oilseed rape (Brassica napus L.)

Background and aims

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture. However, urease, a nickel-dependent enzyme, allows plants to use external or internally generated urea as a nitrogen source. Since a urease inhibitor is frequently applied in conjunction with urea fertilizer, the N-metabolism of plants may be affected. The aim of this study was to determine physiological and molecular effects of nickel deficiency and a urease inhibitor on urea uptake and assimilation in oilseed rape.

Methods

Plants were grown on hydroponic solution with urea as the sole N source under three treatments: plants treated with nickel (+Ni) as a control, without nickel (?Ni) and with nickel and phenylphosphorodiamidate (+Ni+PPD). Urea transport and assimilation were investigated.

Results

The results show that Ni-deficiency or PPD supply led to reduced growth and reduced ¹⁵N-uptake from urea. This effect was more pronounced in PPD-treated plants, which accumulated high amounts of urea and ammonium. Thus, Ni-deficiency or addition of PPD, limit the availability of N and decreased shoot and root amino acid content. The up-regulation of BnDUR3 in roots indicated that this gene is a component of the stress response to nitrogen-deficiency. A general decline of glutamine synthetase (GS) activity and activation of glutamate dehydrogenase (GDH) and increases in its expression level were observed in control plants. At the same time, in (?N) or (+Ni+PPD) treated plants, no increases in GS or GDH activities and expression level were found.

Conclusions

Overall results showed that plants require Ni as a nutrient (while most widely used nutrient solutions are devoid of Ni), whether they are grown with or without a urea supply, and that urease inhibitors may have deleterious effects at least in hydroponic grown oilseed rape.     

Protein secretion in Pseudomonas aeruginosa: characterization of seven xcp genes and processing of secretory apparatus components by prepilin peptidase

The xcp genes are required for the secretion of most extracellular proteins by Pseudomonas aeruginosa. The products of these genes are essential for the transport of exoproteins across the outer membrane after they have reached the periplasm via a signal sequence-dependent pathway. To date, analysis of three xcp genes has suggested the conservation of this secretion pathway in many Gram-negative bacteria. Furthermore, the xcpA gene was shown to be identical to pilD, which encodes a peptidase involved in the processing of fimbrial (pili) subunits, suggesting a connection between pili biogenesis and protein secretion. Here the nucleotide sequences of seven other xcp genes, designated xcpR to -X, are presented. The N-termini of four of the encoded Xcp proteins display similarity to the N-termini of type IV pili, suggesting that XcpA is involved in the processing of these Xcp proteins. This could indeed be demonstrated in vivo. Furthermore, two other proteins, XcpR and XcpS, show similarity to the PilB and PilC proteins required for fimbriae assembly. Since XcpR and PilB display a canonical nucleotide-binding site, ATP hydrolysis may provide energy for both systems.     

Molecular analysis of the modulatory factors of the response to HBsAg in mice as an approach to HBV vaccine enhancement

Abstract Mice were injected with immune complexes containing the recombinant hepatitis B surface antigen (HBsAg) vaccine (S + preS2) bound to different monoclonal antibodies (mAbs), in order to determine whether an enhancement of the response to a human vaccine could be obtained and observed. Enhancement and indifference were observed, as well as a decrease in immunogenicity. N relationship could be established between any effect and affinity or isotypy of the bound mAbs. The preS2 region was rendered more immunogenic when an IgG2a mAb was bound to the S region of the HBsAg. The response to the S region was not modulated, whereas immunogenicity of the preS2 collinear region was decreased by antibody shielding. The mAb which was the most efficient as an enhancer of the antibody response also increased binding of the complexed immunogen to antigen presenting cells. The binding of a human mAb to the sole S region, but not to the preS2 region, should be tested as a potentiating agent of the anti-preS2 human immune response.     

Ants impact the composition of the aquatic macroinvertebrate communities of a myrmecophytic tank bromeliad

In an inundated Mexican forest, 89 out of 92 myrmecophytic tank bromeliads (Aechmea bracteata) housed an associated ant colony: 13 sheltered Azteca serica, 43 Dolichoderus bispinosus, and 33 Neoponera villosa. Ant presence has a positive impact on the diversity of the aquatic macroinvertebrate communities (n = 30 bromeliads studied). A Principal Component Analysis (PCA) showed that the presence and the species of ant are not correlated to bromeliad size, quantity of water, number of wells, filtered organic matter or incident radiation. The PCA and a generalized linear model showed that the presence of Azteca serica differed from the presence of the other two ant species or no ants in its effects on the aquatic invertebrate community (more predators). Therefore, both ant presence and species of ant affect the composition of the aquatic macroinvertebrate communities in the tanks of A. bracteata, likely due to ant deposition of feces and other waste in these tanks.     

Does Manganese Protect Cultured Human Skin Fibroblasts Against Oxidative Injury by Uva, Dithranol and Hydrogen Peroxide?

Reactive oxygen species (ROS) are involved in the mechanism of photoaging and carcinogenesis. Skin is endowed with antioxidant enzymes including superoxide dismutases (SOD): cytosolic copper zinc SOD and mitochondrial manganese SOD. The aim of our study was to estimate the protective effect of manganese against oxidative injury on cultured human skin fibroblasts. Dithranol, hydrogen peroxide and UV-A radiation (375 nm) were employed as oxidative stressors. The supply of manganese chloride produced an increase in cellular content of this element up to 24 fold without concomitant elevation of MnSOD activity. Nevertheless, manganese protects cells against two of the three ROS generating systems assessed, namely hydrogen peroxyde and UV-A. This protective effect depends on the concentration of manganese in the medium, 0.1 mM and 0.2 mM protect against UVA cytotoxicity, only 0.2 mM protects against H₂O₂ cytotoxicity.     

Regulation of cortical dendrite development by Slit-Robo interactions.

Slit proteins have previously been shown to regulate axon guidance, branching, and neural migration. Here we report that, in addition to acting as a chemorepellant for cortical axons, Slit1 regulates dendritic development. Slit1 is expressed in the developing cortex, and exposure to Slit1 leads to increased dendritic growth and branching. Conversely, inhibition of Slit-Robo interactions by Robo-Fc fusion proteins or by a dominant-negative Robo attenuates dendritic branching. Stimulation of neurons transfected with a Met-Robo chimeric receptor with Hepatocyte growth factor leads to a robust induction of dendritic growth and branching, suggesting that Robo-mediated signaling is sufficient to induce dendritic remodeling. These experiments indicate that Slit-Robo interactions may exert a significant influence over the specification of cortical neuron morphology by regulating both axon guidance and dendritic patterning.     

Application of silica aerogel encapsulated lipases in the synthesis of biodiesel by transesterification reactions

Two types of commercial lipases preparations, one from Burkholderia cepacia, the other one from Candida antartica, were encapsulated in silica aerogels reinforced with silica quartz fibre felt and dried by the CO₂ supercritical technique. These immobilized biocatalysts were applied in biodiesel synthesis by transesterification of sunflower seed oil with methyl acetate. They were found to be efficient even with mixtures of both substrates without any solvent addition. The aerogel encapsulation technique made it possible to maintain the enzymes in a dispersion state similar to the dispersion prevailing in an aqueous solution, even for further use in organic hydrophobic media. In transesterification in excess iso-octane, the two lipases encapsulated in aerogels made from 40% MTMS, were found to have activities relatively close to each other and comparable with commercial Novozyme 435. On the other in transesterification with mixture of oil and methyl acetate without any solvent, the kinetics were severely limited by substrate diffusion inside the aerogels. This was particularly true with the C. antartica, so that the corresponding aerogel encapsulated enzyme was much less active than commercial Novozyme 435, although it improved after a few tests.