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  • (Xenopus oocyte)  (1)
  • 1,3-Azaphosphaallyl Anion  (1)
  • Access channel  (1)
  • Barium-bis[N,N′-bis(trimethylsilyl)benzamidinate]  (1)
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  • 1
    ISSN: 1432-1017
    Schlagwort(e): Na-Pump current-voltage relationship ; Na dependence ; Access channel ; N-Terminus truncation ; (Xenopus oocyte)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 0044-2313
    Schlagwort(e): Benzamidinates ; Strontium-bis[N,N′-bis(trimethylsilyl)benzamidinate] ; Barium-bis[N,N′-bis(trimethylsilyl)benzamidinate] ; X-ray Structures ; Spectroscopic Data ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Strontium and Barium Bis[N,N′-bis(trimethylsilyl)benzamidinates] from the Addition Reaction of the Alkaline Earth Metal Bis[bis(trimethylsilyl)amides] and BenzonitrileThe reaction of strontium bis[bis trimethylsilyl)amide] with benzonitrile yields strontium bis[N,N′- bis(trimethylsilyl)benzamidinate] · 2THF, which crystallizes in the orthorhombic space group Pbcn (a = 1845.4(3); b = 131 1,3(2); c = 1838,(3) pm; Z = 4). During the similar reaction of barium bis[bis(trimethylsilyl)amide] with benzonitrile the benzonitrile adduct barium bis[N,N′-bis(trimethylsilyl)benzamidinate] · 2 THF · benzonitrile is formed. After the addition of diphenylacetylene to the strontium di(benzamidinate) in diglyme a clathrate of the composition strontium bis[N,N′-bis(trimethylsilyl)benzamidinate] · diglyme · diphenylacetylene could be isolated; the spectroscopic data as well as the X-ray structure (monoclinic, C2/c, a = 1492.2(2); b = 1539.1(2); c = 2337.8(3)pm; Z = 4) confirm the isolated appearance of the acetylene molecule without interaction to the metal center in solution and in the solid state, respectively.
    Notizen: Bei der Umsetzung des Strontiumbis[bis(trimethylsilyl)amids] mit Benzonitril in THF bildet sich Stronitium-bis[N,N′-bis(trimethylsilyl)benzamidinat] · 2THF, das in der orthorhombischen Raumgruppe Pbcn mit {a = 1 845,4(3); b = 1311,4(2); c = 1838,8(3) pm, Z = 4} kristallisiert. Die entsprechende Reaktion des Barium-bis[bis(trimethylsilyl)amids] mit Benzonitril ergibt das Benzonitril-Addukt Barium bis[N,N′ -bis(trimethylsilyl)benzamidinat] · 2 THF · Benzonitril. Nach der versuchsweisen Umsetzung des Strontium-di(benzamidinats) mit Diphenylacetylen in Diglyme läßt sich ein Clathrat der Zusammensetzung Strontiumbis[N,N′-bis(trimethylsilyl)benzamidinat] · Diglyme · Diphenylacetylen erhalten, dessen spektroskopische und strukturanalytische Untersuchungen (monoklin, C2/c, a = 1492,2(2); b = 1539,1(2); c = 2337,8(3) pm; β = 100,74(1)°; Z = 4) das Vorliegen eines unkomplexierten Diphenylacetylen-Moleküls sowohl in Lösung als auch im Festkörper bestätigen.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 0044-2313
    Schlagwort(e): Barium 1-Aza-3-phosphapropenide ; 1,3-Azaphosphaallyl Anion ; NMR ; X-ray Structure Determination ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Synthesis, NMR Spectroscopic Characterization and Structure of Bis(1,2-dimethoxyethane-O,O′)barium Bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]Barium-bis[bis(trimethylsilyl)phosphanide] 1 reacts with two equivalents of benzonitrile to give barium bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]; the choice of the solvent determines whether a tris-(tetrahydrofuran)- or a bis(1,2-dimethoxyethane)-complex 2 can be isolated. 2 crystallizes from DME as red cuboids (monoclinic, C2/c, a = 1627.0(3), b = 1836.6(3), c = 1602.5(2) pm; β = 96.071(12)°; V = 4761.7(12); Z = 4; wR2 = 0.0851). The phosphorus atom displays a pyramidal surrounding in contrast to the planar coordination sphere of the nitrogen atom. In addition a twist within the P—C—N skeleton of the heteroallyl anion is observed.
    Notizen: Barium-bis[bis(trimethylsilyl)phosphanid] 1 reagiert mit zwei Äquivalenten Benzonitril zu Barium-bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenid]; durch die Wahl des Lösungsmittels läßt sich entweder der Tris(tetrahydrofuran)- oder der Bis(1,2-dimethoxyethan)-Komplex 2 isolieren. Verbindung 2 kristallisiert aus DME in Form roter Würfel aus (monoklin. C2/c, a = 1627,0(3), b = 1836,6(3), c = 1602,5(2) pm; β = 96,071(12)°; V = 4761,7(12); Z = 4; wR2 = 0,0851). Während die Koordinationssphäre des Stickstoffatoms planar ist, befindet sich das Phosphoratom in einer pyramidalen Umgebung. Zusätzlich beobachtet man im 1-Aza-3-phosphapropenid-Anion eine leichte Verdrillung.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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