Search results for "substrate"
showing 10 items of 1018 documents
Temperature–Time Relationship in Collembolan Response to Chemical Exposure
1999
Abstract Effects of temperature on chemical toxicity to a collembolan, Folsomia candida , in relation to time were studied in this experiment. Field soil was used as a test substrate. Collembolans were incubated at three different temperatures (+13, +16, and +19°C) and in two different dimethoate concentrations (1 and 3 mg/kg), clean soil serving as the control. Four destructive samplings were done at 2-week intervals. Dimethoate degradation was also analyzed. Dimethoate 1 mg/kg had a slight effect on both adult growth and reproduction, whereas 3 mg/kg was fatal to F. candida in the soil used. Toxic effects tended to last longer at low temperature than at high temperature, but the differenc…
A novel galactose- and arabinose-specific lectin from the sponge Pellina semitubulosa: isolation, characterization and immunobiological properties.
1992
A new lectin from the sponge Pellina semitubulosa is derived which was extracted and purified to homogeneity. The purified lectin is probably a hexamer of polypeptide chains (each M(r) 34,000) which are covalently linked via disulfide linkages; the isoelectric point is 6.1. The lectin displays the following specificities: D-galactose (50% inhibition of hemagglutination at 0.2 mM) = L-arabinose (0.2 mM) greater than D-fucose (1.5 mM) greater than D-glucose (3.0 mM). It precipitates human erythrocytes (A1, A2, A1B, B, and O) with a titer between 2(8) and 2(11) and erythrocytes from sheep and rabbits with a titer between 2(5) and 2(10). The Pellina lectin displays a strong mitogenic effect on …
Role of Neutral Amino Acid Transport and Protein Breakdown for Substrate Supply of Nitric Oxide Synthase in Human Endothelial Cells
2003
Endothelial dysfunction is often associated with a relative substrate deficiency of the endothelial nitric oxide synthase (eNOS) in spite of apparently high intracellular arginine concentrations. For a better understanding of the underlying pathophysiological mechanisms, we aimed to characterize the intracellular arginine sources of eNOS. Our previous studies in human endothelial EA.hy926 cells suggested the existence of two arginine pools: pool I can be depleted by extracellular lysine, whereas pool II is not freely exchangeable with the extracellular space, but accessible to eNOS. In this study, we demonstrate that the eNOS accessible pool II is also present in human umbilical vein endoth…
Fabrication and Characterization of Epitaxial NbN/TaN/NbN Josephson Junctions Grown by Pulsed Laser Ablation
2009
We report fabrication and characterization of epitaxial NbN/TaN/NbN Josephson junctions grown by pulsed laser ablation. These SNS junctions can be used as elements of rapid-single-flux-quantum (RSFQ) logic, which is a promising technology for high speed digital electronic devices. The NbN/TaN/NbN trilayer films were prepared on a single crystal MgO substrate by pulsed laser ablation, and patterned into junctions using a novel process utilizing e-beam lithography, chemical vapor deposition and e-beam evaporation. The quality of junctions was tested by measuring the temperature dependence of the junctions' IcRn values, observed to be quite close to theoretical values.
Protein Conformational Landscapes and Catalysis. Influence of Active Site Conformations in the Reaction Catalyzed by L-Lactate Dehydrogenase
2015
In the past decade, L-Lactate Dehydrogenase (LDH) has become an extremely useful marker in both clinical diagnosis and in monitoring the course of many human diseases. It has been assumed since the 1980s that the full catalytic process of LDH starts with the binding of the cofactor and the substrate followed by the enclosure of the active site by a mobile loop of the protein before the reaction takes place. In this paper, we show that the chemical step of the LDH-catalyzed reaction can proceed within the open loop conformation, and the different reactivity of the different protein conformations would be in agreement with the broad range of rate constants measured in single-molecule spectrom…
Self-assembly of Organic Molecules on Insulating Surfaces
2015
Molecular self-assembly is known to provide a powerful tool for creating functional structures, with the ultimate structure and functionality encoded in the molecular building blocks. Upon molecule deposition onto surfaces, functional structures have been created ranging from defect-free, highly symmetric two-dimensional layers to complex assemblies with dedicated functionality. Especially organic molecules play a key role for molecular self-assembly due to their impressive structural flexibility and the high degree of control by chemical synthesis. Furthermore, the surface itself provides another exciting dimension: adjusting the subtle balance between intermolecular and molecule-surface i…
Proteomic Analyses Reveal an Acidic Prime Side Specificity for the Astacin Metalloprotease Family Reflected by Physiological Substrates
2011
Astacins are secreted and membrane-bound metalloproteases with clear associations to many important pathological and physiological processes. Yet with only a few substrates described their biological roles are enigmatic. Moreover, the lack of knowledge of astacin cleavage site specificities hampers assay and drug development. Using PICS (proteomic identification of protease cleavage site specificity) and TAILS (terminal amine isotopic labeling of substrates) degradomics approaches >3000 cleavage sites were proteomically identified for five different astacins. Such broad coverage enables family-wide determination of specificities N- and C-terminal to the scissile peptide bond. Remarkably, me…
Processing of procollagen III by meprins: new players in extracellular matrix assembly?
2010
Meprins α and β, a subgroup of zinc metalloproteinases belonging to the astacin family, are known to cleave components of the extracellular matrix, either during physiological remodeling or in pathological situations. In this study we present a new role for meprins in matrix assembly, namely the proteolytic processing of procollagens. Both meprins α and β release the N- and C-propeptides from procollagen III, with such processing events being critical steps in collagen fibril formation. In addition, both meprins cleave procollagen III at exactly the same site as the procollagen C-proteinases, including bone morphogenetic protein-1 (BMP-1) and other members of the tolloid proteinase family. …
Enantioselective addition of nitromethane to α-keto esters catalyzed by copper(ii)–iminopyridine complexes
2008
The copper complex of a chiral iminopyridine easily prepared from (R)-(-)-fenchone and picolylamine catalyzes the enantioselective Henry (nitroaldol) reaction between nitromethane and alpha-keto esters. Good yields and modest to good enantioselectivities are obtained for a wide range of alpha-keto esters, bearing aromatic, alkyl or alkenyl groups attached to the ketone carbonyl group.
Physisorption Instabilities during Dynamic Langmuir Wetting
1994
Continuous dynamic Langmuir wetting of lipid monolayers can create regular stripe patterns on the solid substrate surface. Monolayers doped with minor amounts of fluorescence dye may be deposited in stripes of alternating high and low dye concentration. In case of pure monolayers stripes are observed with AFM. The striations run normal to the dipping direction and have widths of typically several micrometres and distances varying from 1 to ≈ 100 μm. The stripe widths, distances, and fluorescence contrast depend on deposition speed, surface pressure, substrate surface preparation, and dye concentration. The patterns probably result from physisorption (meniscus) instabilities caused by a feed…