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41.
Electrical responses upon mechanostimulation at the posterior cell end were investigated in the marine hypotrichous ciliate Euplotes vannus. A new mechanostimulator was developed to mimic stimuli that are identical with those involved in cell-cell collisions. The receptor potential hyperpolarized by 18–35 mV within 12–25 msec, reached a peak value of -62 mV with a delay of 4–9 msec after membrane deformation, and was deactivated after 50–70 msec. Cirri were stimulated to beat accelerated backward. The corresponding receptor current exerted a similar time course with a peak of 2.4 nA. The shift of the reversal potential by 57.6 mV at a tenfold increase of [K+] 0 identifies potassium ions as current carriers within the development of the receptor potential. An intracellular K concentration of 355 mmol/liter was calculated for cells in a medium that was composed similar to sea-water. The mechanically activated potassium current was totally inhibited by extracellular TEA and intracellular Cs+, and partially inhibited by extracellular 4-AP. The total inhibition of the current by injected EGTA points to a Ca dependence of the posterior mechanosensitivity. It was confirmed by the increase of the peak current amplitude with rising [Ca2+] 0 . Sodium presumably repolarizes the receptor potential because the repolarization was delayed and after-depolarizations were eliminated in media without sodium. Since deciliation did not affect mechano-sensitivity, the corresponding ion channels reside within the soma membrane.The authors wish to thank Mr. Norbert Spreckelmeier from the electronics workshop and Mr. Herbert Lutter from the fine-mechanical workshop of the department for their excellent work, Mrs. G. Key and Mr. H. Mikoleit for skillful technical assistance and for preparing the figures. This work was supported by Deutsche Forschungsgemeinschaft, SFB 171, C7.  相似文献   
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International Microbiology - Acinetobacter baumannii is an opportunistic human pathogen that has become a global threat to healthcare institutions. This Gram-negative bacterium is one of the most...  相似文献   
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We present a proof-of-concept study for production of a recombinant vesicular stomatitis virus (rVSV)-based fusogenic oncolytic virus (OV), rVSV-Newcastle disease virus (NDV), at high cell densities (HCD). Based on comprehensive experiments in 1 L stirred tank reactors (STRs) in batch mode, first optimization studies at HCD were carried out in semi-perfusion in small-scale cultivations using shake flasks. Further, a perfusion process was established using an acoustic settler for cell retention. Growth, production yields, and process-related impurities were evaluated for three candidate cell lines (AGE1.CR, BHK-21, HEK293SF)infected at densities ranging from 15 to 30 × 106 cells/mL. The acoustic settler allowed continuous harvesting of rVSV-NDV with high cell retention efficiencies (above 97%) and infectious virus titers (up to 2.4 × 109 TCID50/mL), more than 4–100 times higher than for optimized batch processes. No decrease in cell-specific virus yield (CSVY) was observed at HCD, regardless of the cell substrate. Taking into account the accumulated number of virions both from the harvest and bioreactor, a 15–30 fold increased volumetric virus productivity for AGE1.CR and HEK293SF was obtained compared to batch processes performed at the same scale. In contrast to all previous findings, formation of syncytia was observed at HCD for the suspension cells BHK 21 and HEK293SF. Oncolytic potency was not affected compared to production in batch mode. Overall, our study describes promising options for the establishment of perfusion processes for efficient large-scale manufacturing of fusogenic rVSV-NDV at HCD for all three candidate cell lines.  相似文献   
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In higher plants, genes for subunits of respiratory chain complex I (NADH:ubiquinone oxidoreductase) have so far been identified solely in organellar genomes. At least nine subunits are encoded by the mitochondrial DNA and 11 homologues by the plastid DNA. One of the 'key' components of complex I is the subunit binding the substrate NADH. The corresponding gene for the mitochondrial subunit has now been cloned and identified in the nuclear genome from potato ( Solanum tuberosum ). The mature protein consists of 457 amino acids and is preceded by a mitochondrial targeting sequence of 30 amino acids. The protein is evolutionarily related to the NADH-binding subunits of complex I from other eukaryotes and is well conserved in the structural domains predicted for binding the substrate NADH, the FMN and one iron-sulphur cluster. Expression examined in different potato tissues by Northern blot analysis shows the highest steady-state mRNA levels in flowers.
Precursor proteins translated in vitro from the cDNA are imported into isolated potato mitochondria in a ΔΨ-dependent manner. The processed translation product has an apparent molecular mass of 55 kDa, identical to the mature protein present in the purified plant mitochondrial complex I. However, the in-vitro translated protein is not imported into isolated chloroplasts. To further investigate whether the complex I-like enzyme in chloroplasts contains an analogous subunit for binding of NAD(P)H, different plastid protein fractions were tested with a polyclonal antiserum directed against the bovine 51 kDa NADH-binding subunit. In none of the different thylakoid or stroma protein fractions analysed were specific crossreactive polypeptides detected. These results are discussed particularly with respect to the structure of a potential complex I in chloroplasts and the nature of its acceptor site.  相似文献   
46.
A new method was developed to purify the streptococcal hyaluronate synthase in active form to electrophoretic homogeneity. The method is based on the extraction of protoplast membranes with digitonin and a phase separation into an aqueous and a detergent phase induced by addition of polyethylene glycol 6000 at 0°C. Proteins bound to hyaluronate were enriched in the aqueous phase, whereas other membrane proteins resided in the detergent phase. Final purification of the hyaluronate synthase was achieved by ion exchange chromatography.  相似文献   
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We shall present several qualitative mathematical models to describe the early evolution of water transport systems in plants. To perform this in a systematic way we apply methods which have been developed in phenomenological synergetics. These methods rest on the fact that it becomes possible to describe the macroscopic behavior of a complex system by a set of control and order parameters when they are suitably identified. Our presentation is addressed to community with interdisciplinary interests.  相似文献   
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Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of 59Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar Km (∼ 10 μM) in both genotypes. In contrast. Vmax was 5.5 μmol Fe-DMA g−1 dry weight [30 min]−1 in Alice, but only 0.6 μmol Fe-DMA g−1 dry weight [30 min]−1 in ysl. Uptake experiments with double-labeled 59Fe-[14C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.  相似文献   
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