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  • 1
    Electronic Resource
    Electronic Resource
    Interaction of transferase II with polynucleotides and inhibition of the interaction by guanosine nucleotides (1971)
    s.l. : American Chemical Society
    Biochemistry 10 (1971), S. 2357-2366 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00788a028
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  • 2
    Electronic Resource
    Electronic Resource
    Structure-function relationships in diphtheria toxin channels: III. Residues which affect the cis pH dependence of channel conductance (1994)
    Springer
    The journal of membrane biology 137 (1994), S. 45-57 
    Details
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Single channel conductance ; Ion selectivity ; pH dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The conductance of channels formed by diphtheria toxin (DT) in lipid bilayer membranes depends strongly on pH. We have previously shown that a 61 amino acid region of the protein, denoted TH8-9, is sufficient to form channels having the same pH-dependent conductance properties as those of whole toxin channels. One residue in this region, Aspartate 352, is responsible for all the dependence of single channel conductance on trans pH, whereas another, Glutamate 349, has no effect. Here, we report that of the seven remaining charged residues in the TH8-9 region, mutations altering the charge on H322, H323, H372, and R377 have minimal effects on single channel conductance; mutations of Glutamates 326, 327, or 362, however, significantly affect single channel conductance as well as its dependence on cis pH. Moreover, Glutamate 362 is titratable from both the cis and trans sides of the membrane, suggesting that this residue lies within the channel; it is more accessible, however, to cis than to trans protons. These results are consistent with the membrane-spanning topology previously proposed for the TH8-9 region, and suggest a geometric model for the DT channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234997
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  • 3
    Electronic Resource
    Electronic Resource
    Structure function relationships in diphtheria toxin channels: II. A residue responsible for the channel's dependence on trans pH (1994)
    Springer
    The journal of membrane biology 137 (1994), S. 29-44 
    Details
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Single channel conductance ; Ion selectivity ; pH dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Ion-conducting channels formed in lipid bilayers by diphtheria toxin are highly pH dependent. Among other properties, the channel's single channel conductance and selectivity depend on proton concentrations on either side of the membrane. We have previously shown that a 61 amino acid fragment of DT is sufficient to form a channel having the same pH-dependent single channel properties as that of the intact toxin. This region corresponds to an a-helical hairpin in the recently published crystal structure of DT in solution; the hairpin contains two α-helices, each long enough to span a membrane, connected by a loop of about nine residues. This paper reports on the single channel effects of mutations which alter the two negatively charged residues in this loop. Changing Glutamate 349 to neutral glutamine or to positive lysine has no effect on the DT channel's single channel conductance or selectivity. In contrast, mutations of Aspartate 352 to neutral asparagine (DT-D352N) or positive lysine (DT-D352K) cause progressive reductions in single channel conductance at pH 5.3 cis/7.2 trans (in 1 m KCl), consistent with this group interacting electrostatically with ions in the channel. The cation selectivity of these mutant channels is also reduced from that of wild-type channels, a direction consistent with residue 352 influencing permeant ions via electrostatic forces. When both sides of the membrane are at pH 4, the conductance difference between wild-type and DT-D352N channels is minimal, suggesting that Asp 352 (in the wild type) is neutral at this pH. Differences observed between wild-type and DT-D352N channels at pH 4.0 cis/7.2 trans (with a high concentration of permeant buffer in the cis compartment) imply that residue 352 is on or near the trans side of the membrane. Comparing the conductances of wild-type and DT-D352K channels at large (cis) positive voltages supports this conclusion. The trans location of position 352 severely constrains the number of possible membrane topologies for this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234996
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  • 4
    Electronic Resource
    Electronic Resource
    Structure-function relationships in diphtheria toxin channels: I. Determining a minimal channel-forming domain (1994)
    Springer
    The journal of membrane biology 137 (1994), S. 17-28 
    Details
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Ion channels ; T-domain ; Channel-forming peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diphtheria Toxin (DT) is a 535 amino acid exotoxin, whose active form consists of two polypeptide chains linked by an interchain disulphide bond. DT's N-terminal A fragment kills cells by enzymatically inactivating their protein synthetic machinery; its C terminal B chain is required for the binding of toxin to sensitive cells and for the translocation of the A fragment into the cytosol. This B fragment, consisting of its N-terminal T domain (amino acids 191–386) and its C-terminal R domain (amino acids 387–535) is responsible for the ion-conducting channels formed by DT in lipid bilayers and cellular plasma membranes. To further delineate the channel-forming region of DT, we studied channels formed by deletion mutants of DT in lipid bilayer membranes under several pH conditions. Channels formed by mutants containing only the T domain (i.e., lacking the A fragment and/or the R domain), as well as those formed by mutants replacing the R domain with Interleukin-2 (Il–2), have single channel conductances and selectivities essentially identical to those of channels formed by wild-type DT. Furthermore, deleting the N-terminal 118 amino acids of the T domain also has minimal effect on the single channel conductance and selectivity of the mutant channels. Together, these data identify a 61 amino acid stretch of the T domain, corresponding to the region which includes α-helices TH8 and TH9 in the crystal structure of DT, as the channel-forming region of the toxin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234995
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  • 5
    Electronic Resource
    Electronic Resource
    Amino acid sequence homology between the enzymic domains of diphtheria toxin and Pseudomonas aeruginosa exotoxin A (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 2 (1988), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Despite similarities In their enzymic properties, diphtheria toxin (DT) and exotoxin A (ETA) of Pseudomonas aeruginosa have major differences in structure and action: consequently, the question of possible evolutionary relatedness of these two proteins remains unanswered. Here we report the existence of significant amino acid sequence homology between the enzymic domain of DT and that of ETA. Iajor segments of sequence may be aligned with high percentages of identity and of conservative substitutions. The homologous stretches in ETA form much of the active-site cleft in the X-ray crystallographic structure. This evidence implies that these domains, at least, have diverged from a common ancestral protein and that active-site residues have been strongly conserved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1988.tb00031.x
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  • 6
    Electronic Resource
    Electronic Resource
    Synchronous Detection by Electron Spin Resonance of Free-Radicals produced at Potential–Modulated Electrodes (1968)
    [s.l.] : Nature Publishing Group
    Nature 220 (1968), S. 155-157 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1. Block diagram of the apparatus. A, Potentiostat amplifier; C, e.s.r. cavity containing electrochemical cell; O, oscilloscope for monitoring the cell polarograph (X and Y are appropriate inputs); P.S.D., phase sensitive or synchronous detector; B,, dual trace pen recorder (numbers refer to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/220155a0
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the sheet resistance of resistive films on thin substrates from 120 to 175 GHz using dielectric waveguides (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 2547-2549 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is reported for the measurement of the sheet resistance, at microwave frequencies, of conducting films supported on thin dielectric substrates. The sheet resistance is found from measurements of the millimeter-wave power transmission through the film using a millimeter-wave source and power meter coupled through dielectric waveguides. The accuracy of this technique does not depend on the precise placement of the waveguide terminations with respect to the substrate, in contrast to methods using metallic waveguides or coils. This method is used to characterize the sheet resistance of semiconductor samples in the frequency range 120–175 GHz and the results are compared to the dc values obtained by conventional techniques. Sheet resistance values can be easily measured by this method in the range from 1 to 1000 Ω. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430534
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  • 8
    Electronic Resource
    Electronic Resource
    Exotoxin A of Pseudomonas aeruginosa: evidence that Domain I functions In receptor binding (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 1 (1987), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have constructed defined deletions in the structural gene of Pseudomonas aeruginosa exotoxin A (ETA) In order to probe the function of Domain t of this protein. Three forms of the gene containing specific deletions were expressed in a strain of Escherichia coli K12 with lesions in the htpR and ion genes; extracts containing the gene products were tested for ADP-ribosylation activity, cytotoxicity, and ability to protect sensitive cells from the cytotoxic action of authentic ETA. Two of the mutant ETAs gave concentration-dependent protection against authentic ETA, and protection correlated with the presence of the bulk of Domain I. The results support the notion that Domain I functions in binding the toxin to specific cell-surface receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1987.tb00528.x
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  • 9
    Electronic Resource
    Electronic Resource
    Anthrax toxin protective antigen: low-pH-induced hydrophobicity and channel formation in liposomes (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: To probe the role of the protective antigen (PA) component of anthrax toxin in toxin entry into animals cells, we examined the membrane channel-forming properties and hydrophobicity of intact and trypsin-cleaved forms of the protein at various pH values. At neutral pH neither form caused release of entrapped K+ from unilamellar lipid vesicles. At pH values below 6.0, however, K+ was rapidly released upon addition of either the nicked PA (PAN) or the 63kDa tryptic fragment of PA (PA63), which has been implicated in the toxin entry process. Under the same conditions intact PA exhibited only weak channel-forming activity, and PA20, the complementary tryptic fragment, showed no such activity. Both PA and PA63 exhibited enhanced hydrophobicity at acidic pH values, but the enhancement was greater and the pH threshold higher with PA63. Our findings indicate that proteolytic removal of PA20 from intact PA enables the residual protein, Pasb63, to adopt a conformation at mildly acidic pH values that permits it to insert readily and form channels in membranes. Thus acidic conditions within endocytic vesicles may trigger membrane insertion of PA63, which in turn promotes translocation of ligated effector moieties, edema factor or lethal factor, across the vesicle membrane into the cytosol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb00796.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of farm and simulated laboratory cold environmental conditions on the performance and physiological responses of lactating dairy cows supplemented with bovine somatotropin (BST) (1990)
    Springer
    International journal of biometeorology 34 (1990), S. 151-156 
    Details
    ISSN: 1432-1254
    Keywords: Bevine somatotropin ; Cold ; Milk production ; Physiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract A study was conducted to evaluate the effect of bovine somatotropin (BST) supplementation in twelve lactating dairy cows maintained in cold environmental conditions. Six cows were injected daily with 25 mg of BST; the other six were injected with a control vehicle. Cows were maintained under standard dairy management during mid-winter for 30 days. Milk production was recorded twice daily, and blood samples were taken weekly. Animals were then transferred to environmentally controlled chambers and exposed to cycling thermoneutral (15° to 20° C) and cycling cold (−5° to +5° C) temperatures for 10 days in a split-reversal design. Milk production, feed and water intake, body weights and rectal temperatures were monitored. Blood samples were taken on days 1, 3, 5, 8 and 10 of each period and analyzed for plasma triiodothyronine (T3), thyroxine (T4), cortisol, insulin and prolactin. Under farm conditions, BST-treated cows produced 11% more milk than control-treated cows and in environmentally controlled chambers produced 17.4% more milk. No differences due to BST in feed or water intake, body weights or rectal temperatures were found under laboratory conditions. Plasma T3 and insulin increased due to BST treatment while no effect was found on cortisol, prolactin or T4. The results showed that the benefits of BST supplementation in lactating dairy cows were achieved under cold environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048712
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