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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 158 (1997), S. 159 -166 
    ISSN: 1432-1424
    Keywords: Key words: Nuclear ion channels — Cation channel — Cell nucleus — Patch clamp — Ion selectivity – Nuclear envelope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Eucaryotic nuclei are surrounded by a double-membrane system enclosing a central cisterna which is continuous with the endoplasmic reticulum and serves as a calcium store for intracellular signaling. The envelope regulates protein and nucleic acid traffic between the nucleus and the cytoplasm via nuclear pores. These protein tunnels cross through both nuclear membranes and are permeable for large molecules. Surprisingly, patch clamp recordings from isolated nuclei of different cell species have revealed a high resistance of the envelope, enabling tight seals and the resolution of single ion channel activity. Here we present for the first time single-channel recordings from nuclei prepared from neuronal tissue. Nuclei isolated from rat cerebral cortex displayed spontaneous long-lasting large conductances in the nucleus-attached mode as well as in excised patches. The open times are in the range of seconds and channel activity increases with depolarization. The single-channel conductance in symmetrical K+ is 166 pS. The channels are selective for cations with P K/P Na= 2. They are neither permeable to, nor gated by Ca2+. Thus, neuronal tissue nuclei contain a large conductance ion channel selective for monovalent cations which may contribute to ionic homeostasis in the complex compartments surrounding these organelles.
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  • 2
    ISSN: 1432-1424
    Keywords: Microglia ; Granulocyte/macrophage colony-stimulating factor ; Whole-cell recording ; Outward K+ currents ; Frequency-independent K+ current ; Peptide toxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Voltage-gated whole-cell currents were recorded from cultured microglial cells which had been developed in the presence of the macrophage/microglial growth factor granulocyte/macrophage colony-stimulating factor. Outward K+ currents (I K) were most prominent in these cells. I Kcould be activated at potentials more positive than −40 mV. Half-maximal activation of I Kwas achieved at −13.8 mV and half-maximal inactivation of I Kwas determined at −33.8 mV. The recovery of I Kfrom inactivation was described by a time constant of 7.9 sec. For a tenfold change in extracellular K+ concentration the reversal potential of I Kshifted by 54 mV. Extracellularly applied 10 mm tetraethylammonium chloride reduced I K by about 50%, while 5 mm 4-aminopyridine almost completely abolished I K. Several divalent cations (Ba2+, Cd2+, Co2+, Zn2+) reduced current amplitudes and shifted the activation curve of I Kto more positive values. Charybdotoxin (IC50 = 1.14 nm) and noxiustoxin (IC50=0.89 nm) blocked I Kin a concentration-dependent manner, whereas dendrotoxin and mast cell degranulating peptide had no effect on the current amplitudes. The outward K+ currents showed a frequency dependence when depolarizing pulses were applied at a frequency of 1 Hz. A frequency-independent outward current (I K′) characterized by the same activation behavior as I Kwas detected. I K′was blocked completely by 10 nm charybdotoxin or by 10 nm noxiustoxin. In contrast to its effect on I K, 10 mm tetraethylammonium chloride did not reduce I K′.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 16 (1988), S. 287-297 
    ISSN: 1432-1017
    Keywords: Ribonuclease T1 ; protein dynamics ; molecular dynamics ; protein-nucleic acid interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Molecular dynamics simulations in vacuum and with a water sphere around the active site were performed on the 2′GMP-RNase T1 complex. The presence of water led to the maintenance of the 2′-GMP-RNase T1 interactions as compared to the X-ray structure, including the hydrogen bonds implicated in the enzyme-inhibitor recognition process. The sidechain of His92 in the molecular dynamics water simulation, however, hydrogen bonds directly to the phosphate of 2′GMP in contrast to the X-ray structure but in support of the role of that residue in the enzyme's catalytic mechanism. Fluctuations of activesite residues are not strongly influenced by water, possibly owing to the exclusion of water by the bound 2′GMP, which did show an increase in mobility. Analysis of the 2′GMP-RNase T1 interactions versus time reveal an equilibrium fluctuation in the presence of water, leading to a less favorable 2′GMP-RNase T1 interaction energy, suggesting a possible relationship between picosecond fluctuations and inhibitor dissociation occurring in the millisecond time domain.
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 468-477 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In an earlier study [Heinemann & Hahn (1992). J. Biol. Chem. 267, 7332–7341], the crystal structure of the double-stranded B-DNA decamer d(CCAGGCm5CTGG) was refined with NUCLSQ to R = 17.4% against 3799 2σ structure amplitudes in the resolution range 8–1.7 Å. This structure has now been re-refined against the same diffraction data using either TNT or X-PLOR in order to determine to what extent the resulting DNA conformations would differ and to examine the suitability of these programs for the refinement of oligonucleotide structures. The R value from the NUCLSQ refinement could not be reached with either TNT or X-PLOR, although both programs yield reasonably refined DNA models showing root-mean-square deviations against the NUCLSQ model of the decamer duplex of 0.25 and 0.32 Å, respectively. Some derived local structure parameters differ depending on the refinement procedure used. This holds true for several exocyclic torsion angles of the sugar-phosphate backbone, whereas sugar puckers as well as helical and base-pair stacking parameters are only weakly influenced. A subset of 15 solvent sites with low temperature factors is conserved in all three models.
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 75-84 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Chloromuconate cycloisomerase (E.C. 5.5.1.7) is an enzyme involved in the 2,4-dichlorophenoxyacetate degradation pathway of Alcaligenes eutrophus JMP134 (pJP4). The crystal structure of this protein was determined at 3 Å resolution by molecular-replacement techniques using atomic coordinates from the reported crystal structure of the homologous muconate cycloisomerase (E.C. 5.5.1.1) from Pseudomonas putida as the search model (42% identical positions in the sequences). Structure refinement by simulated-annealing and restrained least-squares techniques converged at R = 0.195. In the crystals studied, space group I4, the protein is present as two octamers per unit cell with two subunits per asymmetric unit. Each subunit consists of two globular domains, one of which forms an α/β-barrel. Comparison of this structure with that of muconate cycloisomerase reveals the reasons for the altered substrate specificity of chloromuconate cycloisomerase. Marked differences are observed in polarity, accessibility and hydrogen-bonding potential in the channel leading into the active site as well as in the active center itself.
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 871-873 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The acceptor stem of tRNAAla from E. coli has been chemically synthesized and crystallized. This duplex contains a G·U base pair in position 3–70, which is the main identity element for alanyl-tRNA synthetase from E. coli. The crystals are stable in the X-ray beam for a long period of time and diffract to 1.7 Å resolution. The monoclinic crystals reveal a C2 space group with a = 35.0, b = 47.5, c = 26.2 Å, β = 102.3° and one acceptor stem per asymmetric unit.
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  • 7
    ISSN: 0968-0004
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0378-1119
    Keywords: HU ; OmpA signal peptide ; Recombinant DNA ; cassette mutagenesis ; prokaryotic expression
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biophysical Chemistry 50 (1994), S. 157-167 
    ISSN: 0301-4622
    Keywords: Base-pair stacking ; Crystal packing ; DNA double helix ; Sequence-dependent conformation ; X-ray diffraction
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Comparative Biochemistry and Physiology -- Part A: Physiology 93 (1989), S. 195-201 
    ISSN: 0300-9629
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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