Gd5Si2Ge2-based alloys can exhibit a giant magnetocaloric effect (GMCE); this gives them the potential for use in cooling technologies. It has also been reported that a small addition of iron reduces ...the hysteresis losses in Gd5Si2Ge2-based alloys, thus increasing the net refrigerating capacity. In this investigation, we have been the first to look at the effect on the microstructure and magnetic properties of Gd5Si2Ge2 resulting from a wide range of substitutions of Si by Fe. The macrostructures of the arc-melted buttons revealed some very unusual surface morphologies, and the analytical results revealed a gradual substitution of the Gd5(Si,Ge,Fe)4-type phase by a Gd5(Si,Ge,Fe)3-type phase and the presence of three grain-boundary phases, two of which contain substantial amounts of iron. The magnetic measurements indicated that larger amounts of iron reduced the hysteresis losses, but at the same time reduced the Curie temperatures to below lower values that would make the material useful in practice.
Microcystin-LR is the most frequently studied cyclic heptapeptide produced by different genera of cyanobacteria and is hepatotoxic to livestock and human populations. The adverse effects of ...microcystin-LR on morphology and cytoskeletal elements in different stages of early embryonal development have been studied in vitro. Embryos and whole embryo cultures have been exposed to microcystin-LR (10–100 μM). Actin filaments were visualized by fluorescence staining and the microtubular network labelled by immunostaining. Growth, development and cytoskeleton organization of the embryos embedded in
zona pellucida are not affected by microcystin-LR in concentrations up to 100 μM, while whole embryo cell cultures are affected by the presence of microcystin-LR in the culture medium. High microcystin-LR concentrations (100 μM) cause cells to be detached and destroyed, while lower concentrations (10–20 μM) profoundly affect actin and microtubule organization. These effects are confirmed also by the presence of transformed microcystin-LR in all the media at the lowest concentrations. It seems that the changes to the cells are far more serious than that expressed in cell morphology. From our experiments we conclude that the presence of
zona pellucida is an effective way of embryo protection against xenobiotics like microcystin-LR.
The epithelial Na+ channel (ENaC) has a key role in the regulation of extracellular fluid volume and blood pressure. ENaC belongs to a family of ion channels that sense the external environment. ...These channels have large extracellular regions that are thought to interact with environmental cues, such as Na+, Cl−, protons, proteases, and shear stress, which modulate gating behavior. We sought to determine the molecular mechanism by which ENaC senses high external Na+ concentrations, resulting in an inhibition of channel activity. Both our structural model of an ENaC α subunit and the resolved structure of an acid-sensing ion channel (ASIC1) have conserved acidic pockets in the periphery of the extracellular region of the channel. We hypothesized that these acidic pockets host inhibitory allosteric Na+ binding sites. Through site-directed mutagenesis targeting the acidic pocket, we modified the inhibitory response to external Na+. Mutations at selected sites altered the cation inhibitory preference to favor Li+ or K+ rather than Na+. Channel activity was reduced in response to restraining movement within this region by cross-linking structures across the acidic pocket. Our results suggest that residues within the acidic pocket form an allosteric effector binding site for Na+. Our study supports the hypothesis that an acidic cleft is a key ligand binding locus for ENaC and perhaps other members of the ENaC/degenerin family.External Na+ inhibits ENaC.
Mutations centered about a key aspartate in an acidic cleft weakened Na+ inhibition and altered inhibitor selectivity.
The acidic cleft hosts an inhibitory Na+ binding site.
The acidic cleft harbors a key Na+ binding site for ENaC and perhaps sites for ligands that regulate other members of the ENaC/degenerin family.
The aim of this study was to detect cyanobacterial cytoskeletal elements and the cytoskeletal framework using immunostaining with anti-bovine α-tubulin mouse monoclonal antibodies. After strong ...permeabilization of axenic cyanobacterial cell lines, the cytoskeleton elements become visible in all cells. A mild cell permeabilization procedure allows the discrimination between healthy and senescent or otherwise stressed cyanobacteria whose cell integrity has been jeopardized. This technique can be useful to investigate cyanobacterial bloom lysis provoked by various natural or artificial factors. Viruses, among others, are important mortality agents of cyanobacteria. The presence of non-hepatotoxic cyclic cyanopeptides can provoke lysis of non-axenic Microcystis aeruginosa cell lines. This is presumably due to lytic cycle induction in lysogen cyanobacteria. A susceptible cyanobacterial cell line exposed to the depsipeptide planktopeptin BL1125 has been analysed with transmission electron microscopy to corroborate the involvement of virus like particles (VLP) in the process of lysis. VLP that correspond in shape and size to tailed cyanophages have been observed only in samples where the process of lysis has been triggered. The immunostaining of cytoskeletal elements by using epifluorescence and confocal microscopy has confirmed that the lysis expands from single infected cells or cell groups, the focal points, to their immediate environment. Our in vitro experiments demonstrate that lysogen focal point formation, which follows induction by endogenous cyanobacterial cyclic peptides, could constitute, also in the natural environment, the basis for an extremely rapid and extensive cyanobacterial bloom collapse.
The epithelial Na+ channel (ENaC) mediates Na+ transport across high resistance epithelia. This channel is assembled from three homologous subunits with the majority of the protein's mass found in ...the extracellular domains. Acid-sensing ion channel 1 (ASIC1) is homologous to ENaC, but a key functional domain is highly divergent. Here we present molecular models of the extracellular region of α ENaC based on a large data set of mutations that attenuate inhibitory peptide binding in combination with comparative modeling based on the resolved structure of ASIC1. The models successfully rationalized the data from the peptide binding screen. We engineered new mutants that had not been tested based on the models and successfully predict sites where mutations affected peptide binding. Thus, we were able to confirm the overall general fold of our structural models. Further analysis suggested that the α subunit-derived inhibitory peptide affects channel gating by constraining motions within two major domains in the extracellular region, the thumb and finger domains.
Interstitial Sm–Fe-based nitrides with compositions close to that of Sm
2Fe
17N
3 are an interesting class of hard magnetic materials. In this series of experiments we characterised the nitrogenation ...process using a vibrating-sample magnetometer (VSM) and a thermogravimetric differential thermal analyser (TG/DTA). The VSM was fitted with a high-temperature furnace tube and a system for varying the atmosphere around the sample with different gases between 10
−2
mbar and 1
bar. The experiments involved two alloys, with the compositions Sm
13.7Fe
86.3 and Sm
13.8Fe
82.2Ta
4.0, and three different particle sizes, <2
mm, <200, and <15
μm. The results show that the nitriding process is very sensitive to the composition and the particle size, and that nitriding at higher temperatures can result in a nitrogen disproportionation and a loss of the Sm
2Fe
17 phase.
Proteolysis plays an important role in the maturation and activation of epithelial Na+ channels (ENaCs). Non-cleaved channels are inactive at high extracellular Na+ concentrations and fully cleaved ...channels are constitutively active. Cleavage of the α and γ subunits at multiple sites activates the channel through the release of imbedded inhibitory tracts. Peptides derived from these released tracts are also inhibitory, likely through binding at the inhibitory tract sites. We recently reported a model of the α subunit. We have now cross-linked Cys derivatives of the inhibitory peptide to the channel, using our model to predict sites at a domain interface of the α subunit that is in proximity to the N terminus of the peptide. Furthermore, peptide inhibition was mimicked in the absence of peptide by cross-linking the channel across the domain interface. Our results suggest a dynamic domain interface that can be exploited by inhibitory peptides and provides a mechanism for peptide inhibition and proteolytic activation.
Proteases activate ENaC by releasing inhibitory tracts.
Inhibitory peptides cross-link to the finger and thumb domains of ENaC. Simply cross-linking these domains inhibits channel activity.
Inhibitory peptides bind at a finger-thumb interface, inhibiting the channel by maintaining the interface in a tight conformation.
These observations provide insights regarding the mechanisms of channel activation by proteases.
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