Showing papers by "Braunschweig University of Technology published in 1999"
TL;DR: The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency.
Abstract: The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) changes its physical characteristics and biological functions during sperm maturation PHGPx exists as a soluble peroxidase in spermatids but persists in mature spermatozoa as an enzymatically inactive, oxidatively cross-linked, insoluble protein In the midpiece of mature spermatozoa, PHGPx protein represents at least 50 percent of the capsule material that embeds the helix of mitochondria The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency
852 citations
TL;DR: The latest results in tomographic imaging, in which waveforms reflected from an object can be used to form a three-dimensional representation, are described and substantial improvements in the spatial resolution are demonstrated.
Abstract: We review recent progress in the field of terahertz “T-ray” imaging. This relatively new imaging technique, based on terahertz time-domain spectroscopy, has the potential to be the first portable far-infrared imaging spectrometer. We give several examples which illustrate the possible applications of this technology, using both the amplitude and phase information contained in the THz waveforms. We describe the latest results in tomographic imaging, in which waveforms reflected from an object can be used to form a three-dimensional representation. Advanced signal processing tools are exploited for the purposes of extracting tomographic results, including spectroscopic information about each reflecting layer of a sample. We also describe the application of optical near-field techniques to the THz imaging system. Substantial improvements in the spatial resolution are demonstrated.
731 citations
TL;DR: After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil from sand and in combating zoosporic phytopathogens.
Abstract: Biosurfactants containing rhamnose and β-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical properties and potential applications. With Pseudomonas species, more than 100 g l−1 rhamnolipids were produced from 160 g l−1 soybean oil at a volumetric productivity of 0.4 g l−1 h−1. The individual rhamnolipids are able to lower the surface tension of water from 72 mN m−1 to 25–30 mN m−1 at concentrations of 10–200 mg l−1. After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of l-rhamnose, which is already used for the industrial production of high-quality flavor components.
460 citations
TL;DR: Both the pathogen-host and the endophyte-host interactions involve constant mutual antagonisms at least in part based on the secondary metabolites the partners produce, and that of theendophyte and its host is a balanced antagonism.
432 citations
01 Jan 1999
TL;DR: In this paper, a mathematical model for the description of the behavior of viscoplastic materials was developed based on a nonlinear differential equation of order β, where β is a material constant typically in the range 0 < β < 1.
Abstract: The authors have recently developed a mathematical model for the description of the behavior of viscoplastic materials. The model is based on a nonlinear differential equation of order β, where β is a material constant typically in the range 0 < β < 1. This equation is coupled with a first-order differential equation. In the present paper, we introduce and discuss a numerical scheme for the numerical solution of these equations. The algorithm is based on a PECE-type approach.
415 citations
TL;DR: The endosymbiont hypothesis for the origins of plastids (and mitochondria, which will not be further discussed here) was very popular among biologists and fell into disfavour shortly after the First World War and remained scorned for 50 years.
Abstract: That plastids were once free-living cyanobacteria is now taken for granted by many, and for good reasons, for there is a wealth of data – in particular from the comparison of plastid and cyanobacterial genomes – that support this view. There is currently no seriously entertained alternative hypothesis to the view that plastids descend from cyanobacteria. But that was not always the case. Well into the 1970s there was a generally favoured alternative hypothesis, namely that early in evolution plastids arose de novo from within a non-plastid bearing cell (an autogenous origin) rather than through invasion by a cyanobacterium into a non-plastid-bearing cell with subsequent intracellular coexistence and reduction to an organelle (an endosymbiotic origin). Interestingly, the shift from autogenous to endosymbiotic hypotheses during the 1970s was a reversal of state for during the first two decades of this century, the endosymbiont hypothesis for the origins of plastids (and mitochondria, which will not be further discussed here) was very popular among biologists. It fell into disfavour shortly after the First World War, for reasons that are very difficult to summarize briefly, and remained scorned for 50 years (see Sapp, 1994, for an historical account in English, and Hoxtermann, 1998, for a succinct historical account in German). So where did the first version of the endosymbiont hypothesis come from? In a nutshell, it came from Konstantin Sergejewiz Merezkovskij (usually written as Constantin Mereschkowsky), a Russian botanist of little standing who worked at a rather small and by no means prominent university in Kasan and who published a very remarkable paper in 1905. We are not aware of any true precedent for his paper, which draws upon three lines of evidence known at the time.
374 citations
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TL;DR: It is shown how to compute or at least to estimate various capacity-related quantities for bosonic Gaussian channels, including the coherent information, the entanglement-assisted classical capacity, the one-shot classical capacity and a quantity involving the transpose operation, shown to be a general upper bound on the quantum capacity.
Abstract: We show how to compute or at least to estimate various capacity-related quantities for Bosonic Gaussian channels. Among these are the coherent information, the entanglement assisted classical capacity, the one-shot classical capacity, and a new quantity involving the transpose operation, shown to be a general upper bound on the quantum capacity, even allowing for finite errors. All bounds are explicitly evaluated for the case of a one-mode channel with attenuation/amplification and classical noise.
358 citations
TL;DR: The biosynthetic mta gene cluster responsible for myxothiazol formation from the fruiting body forming myxobacterium Stigmatella aurantiaca DW4/3-1 was sequenced and analyzed and provided insight into the mechanism of the formation of the terminal amide of myxOTHiazol.
265 citations
TL;DR: Recent evidence suggests that organelle genomes have persisted because structural proteins that maintain redox balance within bioenergetic membranes must be synthesized when and where they are needed, to counteract the potentially deadly side effects of ATP-generating electron transport.
235 citations
TL;DR: Quantitative estimates of comparatively recent genome flux have profound impact on evolutionary genome comparisons and tend to suggest that a search should be on to identify principles that might ultimately govern gene distribution patterns across prokaryotic genomes.
Abstract: In a recent analysis J.G. Lawrence and H. Ochman [Proc Natl Acad Sci USA 1998;95:9413-9417 (Reference 1)] surmised that about 10% of the current E. coli genome consists of genes that were acquired in over 200 events of lateral gene transfer, which occurred subsequent to the divergence of E. coli and Salmonella some 100 million years ago. Overall, the data suggest that no less than 18% of E. coli's genes might be relatively recent foreign acquisitions, and that the average rate of acquisition may be close to about 16 kb per million years. These quantitative estimates of comparatively recent genome flux have profound impact on evolutionary genome comparisons. They tend to suggest that a search should be on to identify principles that might ultimately govern gene distribution patterns across prokaryotic genomes.
225 citations
TL;DR: In this paper, a numerical model based on rectangular grids is proposed to simulate mixing in aquifers, and the authors show that the model-dependent transverse dispersion caused the modeled plume to degrade much faster and therefore appear much shorter than the actual plume.
TL;DR: These findings suggest that the interaction of PFN II with SMN may be involved in neuron-specific effects of SMN mutations, the primary target of neurodegeneration in SMA.
TL;DR: A series of plasma nitriding experiments has been conducted on AISI 304L austenitic stainless steel at temperatures ranging from 375 to 475°C using pulsed-DC plasma with different pulse duty cycles, N2-H2 gas mixtures and treatment times as mentioned in this paper.
Abstract: A series of plasma nitriding experiments has been conducted on AISI 304L austenitic stainless steel at temperatures ranging from 375 to 475°C using pulsed-DC plasma with different pulse duty cycles, N2–H2 gas mixtures and treatment times. It is shown that a wide range of treatment parameters exist that allow the formation of the S-phase. The formation and growth of this surface layer depend strongly on the treatment parameters, such as nitrogen partial pressure and duty cycle. Within the parameter range investigated, the layer growth appears to be diffusion controlled with an activation energy about 107 kJ/mol. The formation of CrN precipitates during plasma nitriding is not accompanied by the formation of bcc iron, which might be expected due to the loss of free chromium. However, the S-phase transforms into CrN and bcc iron following a heat treatment at 450°C or higher for 25 h. The wear rate after plasma nitriding is greatly reduced compared with the untreated material.
TL;DR: The high mRNA stability under selenium restriction, the speed of biosynthesis upon Selenium repletion and the marginal effect of selenum on the SECIS efficiency indicate that of the GPx isotypes, GI-GPx ranks highest in the hierarchy of seLenoproteins and point to a vital role of GI- GPx in the gastrointestinal tract.
Abstract: The recently described gastrointestinal glutathione peroxidase (GI-GPx) is the fourth member of the family of the selenoenzymes glutathione peroxidases (GPx). In contrast to the more uniform distribution of, for example, the classical glutathione peroxidase (cGPx), it is expressed exclusively in the gastrointestinal tract and has, therefore, been suggested to function as a primary barrier against alimentary hydroperoxides. In order to get an idea of its relative importance we investigated its position in the hierarchy of selenoprotein expression. The selenium-dependent expression of GI-GPx was analyzed in comparison with that of other GPx types at the level of mRNA and protein in HepG2 and CaCo-2 cells. Furthermore, the selenocysteine insertion sequence (SECIS) efficiencies of GI-GPx, phospholipid hydroperoxide glutathione peroxidase (PHGPx) and cGPx in response to selenium were determined by a reporter-gene assay in human hepatoma cells and baby hamster kidney cells. GI-GPx mRNA levels increased during selenium deficiency, whereas cGPx mRNA levels decreased and PHGPx mRNA levels remained almost unaffected. In cells grown in selenium-poor media, all GPx-types were low in both activity and immunochemical reactivity. Upon selenium repletion immunoreactive GI-GPx protein reached a plateau after 10 h, whereas cGPx started to be expressed at 24 h and did not reach its maximum level before 3 days. SECIS efficiencies decreased in the order PHGPx > cGPx > GI-GPx. The augmentation of SECIS efficiencies by selenium was highest for cGPx and intermediate for PHGPx, whereas it was marginal for GI-GPx. The high mRNA stability under selenium restriction, the speed of biosynthesis upon selenium repletion and the marginal effect of selenium on the SECIS efficiency indicate that of the GPx isotypes, GI-GPx ranks highest in the hierarchy of selenoproteins and point to a vital role of GI-GPx in the gastrointestinal tract.
TL;DR: The universal-NOT gate is introduced that takes as an input a qubit in an arbitrary state and generates an output that is as close as possible to the orthogonal state of Psi.
Abstract: Quantum information processing is usually associated with a specific computational basis. Nevertheless, for a deeper understanding of the fundamental principles of quantum computing, it is essential to investigate what is the fidelity of universal operations that are basis independent; i.e., the task is to perform optimally a specific operation on a qubit or a quantum register that is in an unknown state. In this paper we introduce the universal-NOT gate that takes as an input a qubit in an arbitrary state $|\ensuremath{\Psi}〉$ and generates an output that is as close as possible to the orthogonal state $|{\ensuremath{\Psi}}^{\ensuremath{\perp}}〉.$
TL;DR: By generally accepted criteria of target selection and feasibility considerationstryparedoxin and tryparedoxin peroxidase can at present be rated as the most appealing target structures for the development of antiparasitic drugs.
TL;DR: The degradation of EDTA and its metal chelates by different bacterial cultures, catabolic steps in EDTA degradation, and biological methods for the removal of this chelating agent from wastewaters are described.
Abstract: The chelating agent ethylenediaminetetraacetate (EDTA) is not degraded by conventional biological and physicochemical methods for the treatment of wastewater and the purification of drinking water. Of the measurable organic compounds it is the one present at the highest concentration in many surface and drinking waters. In recent years, however, studies have demonstrated that EDTA can be degraded by specially enriched bacterial cultures and in wastewater treatment plants receiving EDTA-containing effluents. The amounts of EDTA released into the aquatic environment could thus be reduced by establishing appropriate biological wastewater treatment plants. This article describes the degradation of EDTA and its metal chelates by different bacterial cultures, catabolic steps in EDTA degradation, and biological methods for the removal of this chelating agent from wastewaters.
TL;DR: It is proposed that the conformational change of vinculin induced by IpaA binding allows interaction of the vinc insulin–IpaA complex with F‐actin and subsequent depolymerization of actin filaments.
Abstract: Shigella flexneri, the causative agent of bacillary dysentery, enters into epithelial cells by a macropinocytic process. IpaA, a Shigella protein secreted upon cell contact, binds to the focal adhesion protein vinculin and is required for efficient bacterial uptake. IpaA was shown here to bind with high affinity to the N-terminal residues 1-265 of vinculin. Using co-sedimentation and solid-phase assays, we demonstrated that binding of IpaA to vinculin strongly increases the association of vinculin with F-actin. We also characterized a depolymerizing activity on actin filaments associated with the vinculin-IpaA complex both in vitro and in microinjected cells. We propose that the conformational change of vinculin induced by IpaA binding allows interaction of the vinculin-IpaA complex with F-actin and subsequent depolymerization of actin filaments.
TL;DR: The marine sponges Ectyplasia perox and Myxilla incrustans were investigated for associated fungal strains and two new compounds, microsphaeropsisin and 2-(1'(E)-propenyl)-octa-4(E),6(Z)-diene-1,2-diol, were obtained.
Abstract: The marine sponges Ectyplasia perox and Myxilla incrustans were investigated for associated fungal strains. Among others, a Coniothyrium sp., from E. perox, and a Microsphaeropsis sp., from M. incr...
TL;DR: It is shown that gephyrin binds with high affinity to molybdopterin, the metabolic precursor of Moco, and expression can reconstitute Moco biosynthesis in Moco-deficient bacteria, a molybdenum-dependent mouse cell line, and a Moco -deficient plant mutant.
Abstract: The molybdenum cofactor (Moco), a highly conserved pterin compound complexing molybdenum, is required for the enzymatic activities of all molybdenum enzymes except nitrogenase. Moco is synthesized by a unique and evolutionarily old pathway that requires the activities of at least six gene products. Some of the proteins involved in bacterial, plant, and invertebrate Moco biosynthesis show striking homologies to the primary structure of gephyrin, a polypeptide required for the clustering of inhibitory glycine receptors in postsynaptic membranes in the rat central nervous system. Here, we show that gephyrin binds with high affinity to molybdopterin, the metabolic precursor of Moco. Furthermore, gephyrin expression can reconstitute Moco biosynthesis in Moco-deficient bacteria, a molybdenum-dependent mouse cell line, and a Moco-deficient plant mutant. Conversely, inhibition of gephyrin expression by antisense RNA expression in cultured murine cells reduces their Moco content significantly. These data indicate that in addition to clustering glycine receptors, gephyrin also is involved in Moco biosynthesis and illustrate the remarkable conservation of its function in Moco biosynthesis throughout phylogeny.
TL;DR: It is reported here that bacterially expressed murine VASP directly interacts with skeletal muscle actin in several test systems including cosedimentation, viscometry and polymerization assays, indicating that the complex formation is primarily based on electrostatic interactions.
TL;DR: In this article, a decision support of automotive engineers by giving an ecological balance of the benefits of substituting ABS by hemp fibres for covering applications is introduced, and the differences of energy demand and emissions amount during the use phase of a passenger car as well as different recycling scenarios are assessed.
Abstract: With the increasing importance of environmental interactions, several innovations of the environmental performance are introduced in automotive industry. One aspect of innovation is an environmental material selection including renewable raw materials. Products of renewable raw materials are generally regarded as environmentally friendly, including products from hemp, jute and flax. The ecological preferences of products of natural fibres can be investigated and described by means of ecological balances. However, no general principles for the ecological advantages or disadvantages of fibre plants can be deducted from their life cycle assessment, since the ecological compatibility of the different products strongly depends on the circumstances of the journey of life of the product. The objective of this study is a decision support of automotive engineers by giving an ecological balance of the benefits of substituting ABS by hemp fibres for covering applications. A Life Cycle Assessment (LCA) of hemp fibre reinforced components is introduced. This study contains the agricultural cultivation of fibre plants, the method of harvesting and the processing of the harvested crops. Finally, the analysis includes the further processing of the fibre, starting from the manufacturing of the fibre composite matrix, on which the production of form press components for the automotive industry bases. The differences of energy demand and emissions amount during the use phase of a passenger car as well as different recycling scenarios are assessed.
TL;DR: The role of the myogenic determination genes as deduced from targeted gene disruptions in mice and how their expression may be controlled are discussed, and recent evidence on genes that play a role in regeneration of muscle in adult organisms is presented.
Abstract: Skeletal muscles in vertebrates develop from somites as the result of patterning and cell type specification events. Here, we review the current knowledge of genes and signals implicated in these processes. We discuss in particular the role of the myogenic determination genes as deduced from targeted gene disruptions in mice and how their expression may be controlled. We also refer to other transcription factors which collaborate with the myogenic regulators in positive or negative ways to control myogenesis. Moreover, we review experiments that demonstrate the influence of tissues surrounding the somites on the process of muscle formation and provide model views on the underlying mechanisms. Finally, we present recent evidence on genes that play a role in regeneration of muscle in adult organisms.
TL;DR: In this article, the authors investigated the band gap structure and integrated density of states for a class of periodic divergence type operators which, in the simplest case, are given by, acting in, and established that Tλ will always have at least one open gap, for λ large (except for trivial cases).
Abstract: We investigate the bandgap structure and the integrated density of states for a class of periodic divergence type operators which, in the simplest case, are given by , acting in . We assume here that ωis an open, connected, periodic subset of and that the complement M ofωdoes not intersect the boundary of the fundamental period cellQ0. Operators of this type occur in simple models for heat conduction or propagation of acoustic waves in a metal with impurities like grains of sand or air bubbles, and in connectiion with photonic crystals. Among other results, we find that Tλ will always have at least one open gap,for λlarge (except for trivial cases).We also establish a connection between the band-gap nstructure of Tλ and the Dirichlet eigenvalue problem on
TL;DR: Analysis of the cDNA for Arabidopsisγ-adaptin and a phylogenetic analysis of all adaptin subunits (proteins) in the context of all known homologous proteins revealed that the large subunits of AP1/2/3 are homologueous and two sub units of the heptameric coatomer I (COPI) complex belong to this gene family.
Abstract: Eukaryotic vesicular transport requires the recognition of membranes through specific protein complexes. The heterotetrameric adaptor protein complexes 1, 2, and 3 (AP1/2/3) are composed of two large, one small, and one medium adaptin subunit. We isolated and characterized the cDNA for Arabidopsisγ-adaptin and performed a phylogenetic analysis of all adaptin subunits (proteins) in the context of all known homologous proteins. This analysis revealed (i) that the large subunits of AP1/2/3 are homologous and (ii) two subunits of the heptameric coatomer I (COPI) complex belong to this gene family. In addition, all small subunits and the aminoterminal domain of the medium subunits of the heterotetramers are homologous to each other; this also holds for two corresponding subunits of the COPI complex. AP1/2/3 and a substructure (heterotetrameric, F-COPI subcomplex) of the heptameric COPI had a common ancestral complex (called pre-F-COPI). Since all large and all small/medium subunits share sequence similarity, the ancestor of this complex is inferred to have been a heterodimer composed of one large and one small subunit. The situation encountered today is the result of successive rounds of coordinated gene duplications of both the large and the small/medium subunits, with F-COPI being the first that separated from the ancestral pre-F-COPI.
TL;DR: In this paper, a new crystallographic model for pure fcc metals in the low temperature range has been developed based on the framework of crystal plasticity and uses the finite element method (FEM).
TL;DR: KCzeta is identified as a component of the upstream kinase responsible for the phosphorylation of the PKCdelta hydrophobic site in vitro and in vivo, antagonizing a rapamycin-sensitive pathway.
TL;DR: From the most extensive screening effort, carried out by the NCl, calanolide A, isolated from the terrestrial plant Calophyllum lanigerum (Guttiferae), has been discovered as the most interesting natural RT inhibitor.
Abstract: Inhibitors of HIV reverse transcriptase (RT) are important drugs for the treatment of acquired immuno-deficiency syndrome (AIDS). One approach to identify novel inhibitors of HIV-1-RT is the screening of natural compounds. Many natural products have been shown to be active as RT inhibitors. These compounds belong to a wide range of different structural classes, e.g., coumarins, flavonoids, tannins, alkaloids, lignans, terpenes, naphtho- and anthraquinones, and polysaccharides. The life forms from which the bioactive compounds were isolated are as equally diverse and comprise terrestrial and marine plants, micro-organisms, and marine animals. From the most extensive screening effort, carried out by the NCl, calanolide A, isolated from the terrestrial plant Calophyllum lanigerum (Guttiferae), has been discovered as the most interesting natural RT inhibitor. The promise of this natural product probably relates to a novel mechanism of action. The current review describes natural products from various sources that are able to inhibit HIV-RT.
TL;DR: An optimal order of convergence is shown for a wide range of two-phase flow problems including heterogeneous media and vanishing capillary pressure in an experimental way and a data parallel implementation of the Newton-multigrid algorithm with speedup results is presented.
TL;DR: In this article, an analysis of scaling effects is performed to evaluate whether data aggregation is a useful regionalization tool or whether it leads to an unacceptable loss of information, in particular, the scale problem of watershed division by a channel network and smaller sub-basins.
Abstract: An analysis of scaling effects is performed to evaluate whether data aggregation is a useful regionalization tool or whether it leads to an unacceptable loss of information. One issue concerns the appropriate resolution of digital elevation models (DEMs) used to derive geomorphological input parameters for hydrological models. In particular, the scale problem of watershed division by a channel network and smaller sub-basins is addressed. The investigation involved commercially available data sets with different horizontal and vertical resolutions and systematically aggregated DEMs. A stream network and the contributing subareas were derived from a DEM with a distinct critical support area. By varying this threshold area various watershed configurations were obtained. The sensitivity of surface runoff simulations to all watershed configurations was studied with synthetic storms and by means of an infiltration excess runoff model.
The study revealed that elevation data with different resolutions diverge enormously in landscape representation and in the derived parameters such as slopes, flow directions and channel networks. Coarse DEMs show a smoother terrain and shorter flow paths than highly resolved data. The contributing threshold area controls the extent of the watershed configuration and therefore determines the drainage density. These topographic and geomorphological features were used to explain differences in the runoff simulation results. When watershed configurations with a varying extent of the channel network were derived from a distinct DEM and then used to simulate surface runoff, the drainage densities of the configurations correlated with the simulated runoff volume. A distinct drainage density, however, did not necessarily lead to similar simulation results when different DEMs were used. Since the hydrological model permits reinfiltration, the runoff volume depends directly on the lengths of the overland flow. Therefore, the mean length of the overland flow paths might to a certain degree be considered as a scaling factor. Copyright © 1999 John Wiley & Sons, Ltd.