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  • 1
    Electronic Resource
    Electronic Resource
    Position-dependent local motions in spin-labeled analogs of a short .alpha.-helical peptide determined by electron spin resonance (1991)
    s.l. : American Chemical Society
    Biochemistry 30 (1991), S. 9498-9503 
    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/bi00103a016
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  • 2
    Electronic Resource
    Electronic Resource
    Side-chain mobility of the .beta.-lactamase A state probed by electron spin resonance spectroscopy (1993)
    s.l. : American Chemical Society
    Biochemistry 32 (1993), S. 5644-5649 
    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/bi00072a021
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  • 3
    Electronic Resource
    Electronic Resource
    Amine and carboxylate spin probe permeability in red cells (1989)
    Springer
    The journal of membrane biology 109 (1989), S. 41-52 
    Details
    ISSN: 1432-1424
    Keywords: EPR spin probe ; membrane permeability ; non-electrolyte ; partition coefficient ; red blood cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Permeabilities for a homologous series of amine and carboxylate nitroxide spin probes were measured in human red blood cells by an electron paramagnetic resonance (EPR) method. Permeabilities determined in this study are much lower than would be predicted for a sheet of bulk hydrocarbon and the polarity of the rate-limiting region is shown to be greater than bulk hydrocarbon. This suggests that the rate-limiting region for permeation of these nonelectrolytes is somewhere in the membrane periphery rather than in the center of the membrane. The red cell membrane does not discriminate between these probes on the basis of molecular volume, as might be predicted by a simple free-volume theory of membrane permeation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870789
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  • 4
    Electronic Resource
    Electronic Resource
    Amine spin probe permeability in sonicated liposomes (1989)
    Springer
    The journal of membrane biology 109 (1989), S. 53-64 
    Details
    ISSN: 1432-1424
    Keywords: EPR spin probe ; liposome ; membrane permeability ; nonelectrolyte ; order parameter ; partition coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Permeabilities for an homologous series of amine nitroxide spin probes were measured in liposomes of varying composition by an electron paramagnetic resonance (EPR) method. Results show that the rate-limiting step in permeation is not adsorption/desorption at the aqueous/membrane interface for two probes in phosphatidylcholine/phosphatidic acid liposomes and for one probe in phosphatidylcholine/cholesterol/phosphatidic acid liposomes. Accordingly, we interpret observed selectivity patterns for the entire series of probes in liposomes and red cells in terms of the properties of the bilayer interior. Results are inconsistent with simple applications of either free volume or hydrocarbon sheet models of nonelectrolyte permeation. In the former case, it was found that liposomes do not select against these probes on the basis of molecular volume. In the latter case, probe permeabilities are all much lower than would be predicted for a sheet of bulk hydrocarbon and the polarity of the rate-limiting region is shown to be greater than bulk hydrocarbon. Together with the results of previous studies of spin-labeled solutes in membranes, as well as studies of lipid dynamics in membranes, these latter results suggest that the rate-limiting region in nonelectrolyte permeation is not in the center of the bilayer, but in the relatively ordered acyl chain segments near the glycerol backbone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870790
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  • 5
    Electronic Resource
    Electronic Resource
    Short alanine-based peptides may form 3 10 -helices and not α-helices in aqueous solution (1992)
    [s.l.] : Nature Publishing Group
    Nature 359 (1992), S. 653-655 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The peptides used are analogues of the alanine-based 3K(I) peptide (which we refer to as 3K-1), which contains three lysine residues in an alanine chain with cysteine as position 1 (ref. 1, and Table 1). The cysteines are introduced to provide an attachment point for the nitroxide ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/359653a0
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  • 6
    Electronic Resource
    Electronic Resource
    Mutations in the M1 region of the nicotinic acetylcholine receptor alter the sensitivity to inhibition by quinacrine (1995)
    Springer
    Cellular and molecular neurobiology 15 (1995), S. 427-438 
    Details
    ISSN: 1573-6830
    Keywords: nicotinic acetylcholine receptor ; quinacrine inhibition ; ion channel ; Torpedo californica ; site directed mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Site directed mutagenesis was used to alter the structure ofTorpedo californica nicotinic acetylcholine receptor (nAChR) and to identify amino acid residues which contribute to noncompetitive inhibition by quinacrine. Mutant receptors were expressed inXenopus laevis oocytes injected within vitro synthesized mRNA and the whole cell currents induced by acetylcholine (ACh) were recorded by two electrode voltage clamp. 2. A series of mutations of a highly conserved Arg at position 209 of theα subunit ofTorpedo californica nAChR revealed that positively charged amino acids are required for functional receptor expression. Mutation of Arg to Lys (αR209K) or His (αR209H) at position 209 shifted the EC50 for ACh slightly from 5µM to 12µM and increased the normalized maximal channel activity 8.5-and 3.2-fold, respectively. 3. These mutations altered the sensitivity of nAChR to noncompetitive inhibition by quinacrine. The extent of inhibition of ion channel function by quinacrine was decreased as pH increased in both wild type and mutant nAChR suggesting that the doubly charged form of quinacrine was responsible for the inhibition. 4. Further mutations at different positions of theα subunit suggest the contribution of Pro and Tyr residues at positions 211 and 213 to quinacrine inhibition whereas mutationsαI210A andαL212A did not have any effects. None of these mutations changed the sensitivity of nAChR to inhibition by a different noncompetitive inhibitor, chlorpromazine. 5. These findings support a hypothesis that the quinacrine binding site is located in the lumen of the ion channel. In addition, the quantitative effect of point mutations at alternate positions on the sensitivity of quinacrine inhibition suggests that the secondary structure at the beginning of M1 region might beβ sheet structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02071878
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  • 7
    Electronic Resource
    Electronic Resource
    Site-directed mutagenesis of colicin E1 provides specific attachment sites for spin labels whose spectra are sensitive to local conformation (1989)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 6 (1989), S. 294-305 
    Details
    ISSN: 0887-3585
    Keywords: α-helix ; EPR ; trypsinolysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Colicin E1 is an E. coli plasmid-lencoded water-soluble protein that spontaneously inserts into lipid membranes to form a voltage-gated ion channel. We have employed a novel approach is which site-directed mutagenesis is used to provide highly specific attachment points for nitroxide spin labels. A series of colicin mutants, differing only by the position of a single cysteine residue, were prepared and selectively labeled at that cysteine. A hydrophilic sequence (398-406) within the C-terminal domain of the water-soluble form of the protein was investigated and exhibited an electron paramagnetic resonancc (EPR) spectral periodicity strongly suggesting an amphiphilic α-helix. After removal of the N—terminus of the protein with trypsin, the spectra for this sequence indicate increased label mobility and a more flexible structure.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340060312
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  • 8
    Electronic Resource
    Electronic Resource
    A single tryptic fragment of colicin E1 can form an ion channel: Stoichiometry confirms kinetics (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 254-262 
    Details
    ISSN: 0887-3585
    Keywords: EPR ; molecularity ; colicin E1 ; ion channel ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The molecularity of the ion channel formed by peptide fragments of colicin has taken on particular significance since the length of the active peptide has been shown to be less than 90 amino acids and the lumen size at least 8 Å. Cell survival experiments show that killing by colicin obeys single-hit statistics, and ion leakage rates from phospholipid vesicles are first order in colicin concentration. However, interpretation in molecular terms is generally complicated by the requirement of large numbers of colicin molecules per cell or vesicle.We have measured the discharge of potential across membranes of small phospholipid vesicles by following the changes in binding of potential sensitive spin labeled phosphonium ions as a function of the number of colicin fragments added. Because of the sensitivity of the method, it was possible to reliably investigate the effect of colicin in a range where there was no more than 0.2 colicins per vesicle. The quantitative results of these experiments yield a direct molecular stoichiometry and demonstrate that one C-terminal fragment of the colicin molecule per one vesicle is sufficient to induce a rapid ion flux in these vesicles. In addition, the experiments confirm earlier findings that the colicin fragments do not migrate from one vesicle to another at pH 4.5. Similar results are obtained with large unilamellar vesicles.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110404
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