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  • 1
    Electronic Resource
    Electronic Resource
    Voltage-dependent inhibition of the sodium pump by external sodium: Species differences and possible role of the N-terminus of the α-subunit (1993)
    Springer
    European biophysics journal 21 (1993), S. 433-443 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185871
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  • 2
    Electronic Resource
    Electronic Resource
    Synthese und Molekülstruktur von Barium-bis[N,N′-bis(trimethylsilyl)benzamidinat] · DME · THF (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 1455-1461 
    Details
    ISSN: 0044-2313
    Keywords: Barium-bis[N,N′-bis(trimethylsilyl)benzamidinate] · DME · THF ; Benzamidinate ; X-ray Structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis and Molecular Structure of Barium Bis[N,N′-bis(trimethylsilyl)benzamidinate] ° DME ° THFBarium bis[N,N′-bis(trimethylsilyl)benzamidinate] · thf · dme crystallizes in the monoclinic space group P21/n with a = 1 122.0(2), b = 2 190.7(4), c = 1 840.2(3) pm, β = 98.04(1)° and Z = 4 containing a metal center in a distorted monocapped trigonal prismatic surrounding. The barium dibenzamidinate moiety is sent with an angle of 120°, although this leads to different Ba—N distances of 273 and 282 pm originating from the interligand repulsion of the trimethylsilyl groups and the dme substituent. The 1,3-diazaallyl fragment with C—N bond lengths of 132 pm shows a delocalisation of the anionic charge.
    Notes: Barium-bis[N,N′-bis(trimethylsilyl)-benzamidinat] · DME · THF kristallisiert in der monoklinen Raumgruppe P21/n mit a = 1 122,0(2), b = 2 190,7(4), c = 1 840,2(3) pm, β = 98,04(1)° und Z = 4 mit einem Metallzentrum in einer einfach überdachten, verzerrt prismatischen Umgebung. Die Barium-dibenzamidinat-Substruktur ist mit einem Winkel von 120° gewinkelt, die zwei jeweils verschiedenen Ba—N-Abstände von 273 und 282 pm rühren von der sterischen Hinderung zwischen den Trimethylsilyl-Gruppen und dem DME-Liganden her. Das 1,3-Diazaallyl-Fragment weist mit C—N-Bindungslängen von 132 pm eine Delokalisation der anionischen Ladung auf.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190822
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  • 3
    Electronic Resource
    Electronic Resource
    Molekül- und Kristallstruktur von Magnesium-bis[bis(trimethylsilyl)phosphanid] · DME (1994)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 304-308 
    Details
    ISSN: 0044-2313
    Keywords: Magnesium Bis[bis(trimethylsilyl)phosphide] · DME ; Phosphide ; X-ray Structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Molecular and Crystal Structure of Magnesium Bis[bis(trimethylsilyl)phosphide] · DMEMagnesium bis[bis(trimethylsilyl)phosphide] crystallizes in the tetragonal space group I4c2 with a = 1652.9(2); c = 2282.6(5) pm and Z = 8. The magnesium atom is distorted tetrahedrally surrounded by two oxygen and two phosphorus atoms with Mg—P- and Mg—O-bond lengths of 248.7(2) and 204.7(5) pm, respectively. The phosphorus atom displays a trigonal pyramidal coordination.
    Notes: Magnesium-bis[bis(trimethylsilyl)phosphanid] · DME kristallisiert in der tetragonalen Raumgruppe I4c2 mit a = 1652,9(2); c = 2282,6(5) pm und Z = 8. Das Magnesiumatom ist von zwei Sauerstoff- und zwei Phosphoratomen mit Mg—P- und Mg—O-Bindungslängen von 248,7(2) bzw. 204,7(5) pm verzerrt tetraedrisch umgeben. Das Phosphoratom ist trigonal pyramidal koordiniert.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19946200215
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