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  • 1
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Electron dense deposits (EDD) were observed on the extracellular side of the plasmalemma of Chara internodal cells by a calcium-glutaraldehyde fixation technique. The number and size of EDD were greatly increased when cells had been preincubated in Ca2+-enriched medium before fixation. The addition of Na+, Mg2+, or La3+ instead of Ca2+ in incubation and fixation media produced no deposits at all, Sr2+ caused deposits with similar distribution to those formed by Ca2+, and Ba2+ addition resulted in deposits localized at different sites within the cell. Microprobe analysis of single EDD from Ca2+ incubated cells ascertained the presence of calcium in these deposits. Possible functions of the Ca2+-binding sites at the plasma membrane of Chara cells are discussed.
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  • 2
    ISSN: 1612-1112
    Keywords: Chloride distribution coefficient ; Co-ion dependence ; Halide selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dependence of the chloride distribution coefficient on the co-ion of solutions of different alkali fluorides, MF, up to 11M is tested on the strongly basic anion-exchange resin AG1-X10. Under the same experimental conditions the distribution coefficient decreases in the following order for M+: Na+〉K+〉Rb+〉Cs+. This can be explained by the different co-ion-chloride interactions. The consequence of this interaction for a chromatographic separation of chloride is shown with 5M KF and CsF solutions, used as eluants. Depending on the fluoride concentration, the distribution coefficient passes through a minimum value to increase again at higher electrolyte concentration. The non-exchange electrolyte in the resin phase is responsible for this effect. In addition, the bromide and the iodide distribution coefficients up to 10M KF solutions are determined. One results is that the selectivity coefficient between halide ions increases at higher electrolyte concentrations.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary All bacterial strains classified into the family Rhizobiaceae can be induced to undergo a fundamental genome rearrangement. The special structure of their genome allows the formation of five distinctive phenotypes, each one adapted to a different habitat (Fig. 1). This genome rearrangement can be induced by DNA-damaging agents, UV irridiation or chemical mutagenesis. For expression, cells have to be protected against photorepair and their replication has to be reduced by stress treatment. The rearrangement process is, with special exceptions, reversible. Classes I and II comprise Agrobacteria and Rhizobia, class III nitrogen-fixing strains and classes IV and V two different carotenoid-pigmented types. One of the class V strains has been shown to be an effective legume-symbiont. DNA characteristics and inter-class hybridization results show not only that the genomes are completely reconstructed during each step of rearrangement, but also that the bacteria of all five classes are genetically correlated. In many cases the genetic label has been maintained during rearrangement into the different classes. The identity of each class is protected by a class-specific restriction and modification system, which was analyzed by phage typing experiments and by functional analysis of class-specific restriction endonucleases. We propose to designate the classes as different species of Rhizobiaceae. The unidirectional rearrangement between nodulating Rhizobia and tumorgenic Agrobacteria has been interpreted as a sequence of decreasing complexity of genomic regions coding for the plant interactions of these bacteria.
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    ISSN: 1520-5142
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1744-313X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Induction of tolerance to bovine serum albumin was studied in mice selected for high (H) or low (L) antibody responsiveness and in their F1 hybrids. No high or low zone tolerances were obtained in H mice whereas L mice were susceptible to tolerance induction by the two schedules. H mice were immunized by repeated injections of tolerogenic BSA for low zone tolerance induction but not after the administration of a single high dose of tolerogenic BSA. Resistance to tolerance induction is dominant in F1 hybrids.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 292 (1981), S. 838 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Guinea pig erythrocyte ghosts loaded with NGF or NGF antibodies (see Fig. 2 legend) served as vehicles for injecting these molecules into the cytoplasm of NGF target cells through cell fusion. The target cells were a line of PC 12 phaeochromocytoma cells which reacted rapidly to NGF with an ...
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  • 7
    ISSN: 1573-8647
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
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  • 8
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Bei Erzeugung negativer Thermionen im Massenspektrometer wird eine Meßtechnik zur genauen Isotopenverhältnisbestimmung 129I/127I entwickelt. Die Anwendung der Isotopenverdünnungsanalyse unter Verwendung eines Indicators, der an dem langlebigen radioaktiven 129I-Isotop angereichert ist, ermöglicht in diesem Zusammenhang auch eine vergleichsweise richtige Iodspurenbestimmung mit dem Massenspektrometer. In verschiedenen, handelsüblichen Speisesalzen sowie in zwei Reinchemikalien werden Iodspuren mit der massenspektrometrischen Isotopenverdünnungsanalyse bestimmt, wobei relative Standardabweichungen von etwa 1,5 % im unteren ppm-Bereich erreicht werden. Die Nachweisgrenze des beschriebenen Verfahrens, welches die Summe aller anorganischen Iodspecies erfaßt, liegt bei 6 ppb. Die zum analytischen Vergleich durchgeführten Bestimmungen mit einer iodidselektiven Elektrode zeigen gute Übereinstimmung der Ergebnisse. Die chemische Abtrennung des Iodidions geschieht mit der Anionenaustausch-Chromatographie.
    Notes: Summary A technique for a precise isotope ratio measurement of 129I/127I is developed in the mass spectrometer by negative thermal ionization. The application of the isotope dilution technique using a spike which is enriched in the longlived radioactive 129I isotope opens the possibility for an accurate iodine trace analysis by mass spectrometry. Different commercially available table salts as well as two pure chemicals are determined for iodine traces by mass spectrometric isotope dilution analysis. Relative standard deviations of about 1.5 % are obtained in the lower ppmrange. The detection limit of this method which analyses the sum of all inorganic species is 6 ppb. For an analytical comparison the same samples are analysed using an iodideselective electrode. The results agree well with the mass spectrometric values. The chemical separation of the iodide ion is carried out by anion-exchange chromatography.
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  • 9
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird ein Verfahren der massenspektrometrischen Isotopenverdünnungsanalyse sowie eine Messung mit ionenselektiver Elektrode nach chromatographischer Abtrennung zur Bromid-Spurenbestimmung in geologischen Proben beschrieben. Während für erstgenannte Methode ein saurer Aufschluß mit HF Verwendung findet, wird beim zweiten Verfahren ein alkalischer Schmelzaufschluß mit einer Na2CO3/ZnO-Mischung benutzt. Für die Isotopenverhältnismessung79Br/81Br werden negative Thermionen im Massenspektrometer erzeugt. Anhand der Analyse einiger geochemischer Standards des „Centre de Recherches Pétrographiques et Géochimiques“ ergibt sich eine sehr gute Übereinstimmung beider Verfahren im unteren ppm-Bereich. Dabei ist die Isotopenverdünnungstechnik besonders als Eichmethode geeignet.
    Notes: Summary Methods for the determination of bromide traces in geological samples with isotope dilution mass spectrometry and with an ion-selective electrode after chromatographic separation are described. For the mass spectrometric method, an acidic decomposition of the sample with HF is carried out, for the electrochemical analysis the sample is melted in a mixture of Na2CO3/ZnO. The isotope ratio79Br/81Br is determined by producing negative thermal ions in the mass spectrometer. Analyses of some geochemical standards from the “Centre de Recherches Pétrographiques et Géochimiques” show very good agreement in the lower ppm range with both methods. The isotope dilution technique is especially suitable as a calibration method.
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  • 10
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Macronuclear DNAs from three related hypotrichous ciliated protozoans were compared by agarose gel electrophoresis. Each was shown to be composed of DNA duplexes that yielded a unique pattern of bands overlying a continuous distribution of DNA sizes ranging from ∼400 bp to ∼20,000 bp. By EM, the number average molecular sizes for doublestranded DNA were 2,200 bp for Oxytricha sp., 2,514 bp for Stylonychia pustulata and 1,836 bp for Euplotes aediculatus. Contrary to previous reports we present evidence that the macronuclear DNAs in each of these three organisms lack single-stranded interruptions.
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