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  • 1
    ISSN: 1432-1017
    Keywords: Na-Pump current-voltage relationship ; Na dependence ; Access channel ; N-Terminus truncation ; (Xenopus oocyte)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Currents generated by the Na+/K+ ATPase were measured under voltage clamp in oocytes of Xenopus laevis. The dependence of pump current on external [Na+] was investigated for the endogenous Xenopus pump as well as for wild-type and mutated pumps of electroplax of Torpedo californica expressed in the oocytes. The mutants had α-subunits truncated before position Lys28 (αΔK28) or Thr29 (αΔT29) of the N-terminus. The currents generated by all variants of pump molecules in the presence of 5 mM K+ show voltage-dependent inhibition by external [Na+]. The apparent K1 values increase with membrane depolarisation, and the potential dependence can be described by the movement of effective charges in the electrical potential gradient across the membrane. Taking into account Na+-K+ competition for external binding to the E2P form, apparent K1 values and effective charges for the interaction of the Na+ ions with the E2P form can be estimated. For the Xenopus pump the effective charge amounts to 1.1 of an elementary charge and the K1 value at 0 mV to 44 mM. For the wild-type Torpedo pump, the analysis yields values of 0.73 of an elementary charge and 133 mM, respectively. Truncation at the N-terminus removing a lysinerich cluster of the a-subunit of the Torpedo pump leads to an increase of the effective charge and decrease of the K1 value. For αΔK28, values of 0.83 of an elementary charge and 117 mM are obtained, respectively. If LyS28 is included in the truncation (α·T29), the effective charge increases to 1.5 of an elementary charge and the apparent K1 value is reduced to 107 mM. The K, values for pump inhibition by external Na+, calculated by taking into account Na+-K+ competition, are smaller than the K/12 values determined in the presence of 5 mM [K+]. The difference is more pronounced for those pump variants that have higher Km, values. The variations of the parameters describing inhibition by external [Na+] are qualitatively similar to those described for the stimulation of the pumps by external [K+] in the absence of extracellular [Na+]. The observations may be explained by an acess channel within the membrane dielectric that has to be passed by the external Na+ and K+ ions to reach or leave their binding sites. The potential-dependent access and/or the interaction with the binding sites shows species differences and is affected by cytoplasmic lysine residues in the N-terminus.
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  • 2
    ISSN: 1420-8903
    Keywords: Primary 11K65 ; Secondary 11N37, 11A25, 43A60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Still another proof is given for Parseval's well-known equation $$\sum\limits_{1 \leqslant r〈 \infty } {|a_r |^2 \cdot \varphi (r) = \parallel f\parallel \begin{array}{*{20}c} 2 \\ 2 \\ \end{array} } $$ forB 2-almost-even arithmetical functionsf with Ramanujan coefficients $$a_r = \frac{1}{{\varphi (r)}} \cdot M(f \cdot c_r )$$ . An explicit “best approximation” off by even functions, constructed from characteristic functions of subsets {n; g.c.d.(n, r) =k} ⊂ $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{\mathbb{N}} $$ is used.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 21 (1970), S. 157-166 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The Clostridium thermocellum cellulase genes celA and celC encoding endoglucanase A and C were subcloned in a temperature-regulated Escherichia coli expression vector containing the leftward promoterpl of bacteriophage lambda. The level of gene expression was controlled by thermal inactivation of the heat-sensitive lambda cI857 repressor. Under optimal conditions the recombinant endoglucanases A and C were expressed to a level of 10–15% of total cellular protein. Endoglucanase A was partially exported into the periplasmic space, whereas endoglucanase C was found sequestered within the cytoplasm. Overexpression of the celA gene resulted in decreased cell viability concomitant with the accumulation of endoglucanase A in the membrane fraction. In contrast, high-level synthesis of the celC gene product was well tolerated by the host cell. Overproduced endoglucanase C accumulated as a soluble enzyme without detectable formation of inactive inclusion bodies.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Endoglucanase C encoded by the celC gene of Clostridium thermocellum has been purified to homogeneity from a recombinant Escherichia coli strain. It was found that this enzyme is highly efficient in degrading glucans with alternating β-1,4- and β-1,3-linkages but lacks activity on unmodified cellulosic substrates. The properties of endoglucanase C were compared to those of Bacillus subtilis β-glucanase, an enzyme used in the brewing industry for β-glucan degradation. Both enzyme cause a rapid decrease of the viscosity of barley β-glucan as a result of internal chain cleavage. Endoglucanase C hydrolyses non-specifically β-1,3- and β-1,4-bonds adjacent to unsubstituted or 4-O′-substituted cellobiose units. Due to its lower pH optimum and increased thermostability endoglucanase C compares favourably with B. subtilis β-glucanase and seems suitable for use in the mashing process of beer brewing.
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  • 7
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Exact predictions for two-pulse visual temporal integration data are derived from the Bouman-van der Velden quantum coincidence model for threshold vision. The predictions of the model start with complete summation for superposed pulses, then pass to a transition zone of partial integration, and finally reach the level of probability summation for pulses presented with large interstimulus intervals. From our results we can clearly reject the assumption of constant integration times with the basic model. We thus generalize the coincidence model to allow for variable integration times, derive the corresponding predictions for two-pulse integration data, and compare these predictions to published data currently available. It is shown that detectors of low order of coincidence generally underestimate the actual reduction of threshold intensity (or equivalently the corresponding increase of the detection probability) for two pulses as compared to the singlepulse performance.
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  • 8
    ISSN: 1434-4475
    Keywords: Halogen exchange, in pyrimidines ; Pyrimidines, 5-ethylsulfonyl-methyl- ; Pyrimidines ; 5-ethylthiomethyl-
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In 2,4-dichloro-5-ethylthiomethylpyrimidines3a, b and in (2,4-dichloro-5-pyrimidinylmethyl)ethyl sulfones5a, b, resp., by reaction with ammonia, diethyl-amine, isopropylamine, sodium methanolate and sodium ethylthiolate, resp., the halogen atoms have been substituted by amino, methoxy or ethylthio groups, resp., and thus the compounds4a–4r and5c–5f have been obtained.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 23 (1972), S. 251-256 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 23 (1972), S. 408-409 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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