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  • Polymer and Materials Science  (7)
  • Atomic, Molecular and Optical Physics  (2)
  • dynamic channel  (1)
  • metastable states  (1)
  • peptide libration mechanism  (1)
  • quadrupolar nuclear magnetic resonance  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    Temperature dependence of single channel currents and the peptide libration mechanism for ion transport through the gramicidin A transmembrane channel (1984)
    Springer
    The journal of membrane biology 81 (1984), S. 205-217 
    Details
    ISSN: 1432-1424
    Schlagwort(e): gramicidin channel ; temperature dependence ; single channel current histograms ; peptide libration mechanism ; nonlinear Arrhenius plots ; metastable states ; dynamic channel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Summary A study of the temperature dependence of gramicidin A conductance of K+ in diphytanoyllecithin/n-decane membranes shows the plot of In (single channel conductance) as a function of reciprocal temperature to be nonlinear for the most probable set of conductance, states. These results are considered in terms of a series of barriers, of the dynamics of channel conformation,vis-a-vis the peptide libration mechanism, and of the effect of lipid viscosity on side chain motions again as affecting the energetics of peptide libration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01868714
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  • 2
    Digitale Medien
    Digitale Medien
    Potassium-39 NMR of K+ interaction with the gramicidin channel and NMR-derived conductance ratios for Na+, K+ and Rb+ (1986)
    Springer
    The journal of membrane biology 89 (1986), S. 107-111 
    Details
    ISSN: 1432-1424
    Schlagwort(e): quadrupolar nuclear magnetic resonance ; rotational correlation times and off-rate constants ; potassium-39 NMR ; gramicidin channel transport ; ion transport specificity ; electrophysiology without electrodes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Summary A potassium-39 NMR study of potassium ion interaction with the gramicidin transmembrane channel in phospholipid bilayers at high ion activity is reported which allows determination of a weak binding constant, K b w ≃8.3/m, and an off-rate constant for the weak site,k off w ≃2.6×107/sec. These values are interpreted with the aid of additional NMR data as the binding constant for formation of the doubly occupied channel state and the rate constant for an ion leaving the doubly occupied state. Considering the singly occupied channel state for the potassium ion to be “electrically silent” at 1 molar ion activity, as with the sodium ion, the single-channel conductance for 100 mV and 30°C calculated to be 29 pS, and using the same approximation with previous NMR results on the sodium and rubidium ions, reasonable conductance ratios were calculated. Further experimental estimates of the other three constants with the experimental location of binding sites and Eyring rate theory to introduce voltage dependence allowed a more complete calculation of the two-site channel. The single-channel conductance for potassium ion is calculated to be 24 pS at 1m activity and 26 pS at 0.6m activity, which compares for diphytanoyl phosphatidylcholine membranes to an experimental most probable single-channel conductance of 25 pS and a mean channel conductance of 20 pS. The calculated conductance ratios using NMR-derived constants were γ(K)/γ(Na)=2.0 and γ(Rb)/γ(Na)=4.3. These results are close to the experimental values and provide further basis for the use of NMR of quadrupolar ions to provide information on the ionic mechanism of channel transport.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01870900
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  • 3
    Digitale Medien
    Digitale Medien
    A theoretical estimate of the energy barriers between stable conformations of the proline dimer (1975)
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 1121-1132 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Semi-empirical energy calculations for an internal Pro-Pro dimer are presented that take into account the nature of the flexibility of the proline ring due to its puckering. Calculations show that three stable conformations are available for the dimer: the cis (ω = 0°, ψ = 160°); the trans (ω = 180°, ψ = 160°, also referred to as trans′); and the cis′ (ω = 180°, ψ = -40°) conformations. The best conformational pathways between these stable conformations are determined. Calculations also show that the barrier for cis′-trans′ conversion is of the same order of magnitude as that for cis-trans conversion.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1975.360140602
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  • 4
    Digitale Medien
    Digitale Medien
    Stereochemical criteria for polypeptides and proteins. IV. Standard dimensions for the cis-peptide unit and conformation of cis-polypeptidesContribution No. 232 from the Centre of Advanced Study in Physics, University of Madras, Madras-25, India. For Part III see Ramachandran et al. (1968)
    New York : Wiley-Blackwell
    Biopolymers 6 (1968), S. 1255-1262 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using potential energy formulas for variation of bond angles and for ω-distortion, the conformation of minimum energy for the cisform of the petide unit has been worked out. This agrees very well with the corresponding set of atoms in the crystal structure of Leu-Pro-Gly and the dimensions of a standard cispeptide unit are given based on these. The conformational (φ,Ψ) map for a cispeptide unit has been worked out from contact criteria, both for a pair of linked units as well as for-helices having constant (φ,Ψ). The small allowed region of the helical map contains the conformation experimentally observed for poly-L-proline I.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1968.360060903
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  • 5
    Digitale Medien
    Digitale Medien
    The Leu5 gramicidin a analog: Molecular mechanics calculations and analysis of single channel steps related to multiplicity of conducting states (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 315-326 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Single-channel studies have shown that there exist a multiplicity of conducting states in Gramicidin A (GA). In an earlier work presented at this symposium, it was proposed that such a multiplicity may be expected from different long-lived side-chain distributions available for the channel molecule. In order to test this hypothesis, Leu5-Gramicidin A was synthesized and the effect of replacing the L · Ala5 residue by L · Leu5 was analyzed. First, molecular mechanics calculations on Leu5-Gramicidin A are presented. Then the single-channel conductance sweeps obtained for Leu5-GA are automatically analyzed in the computer using specifically developed algorithms. The results show a dramatic decrease in the multiplicity of states due to the Leu5 substitution. This experimental result is discussed in the light of structural concepts emerging from molecular mechanics calculations.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560260733
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  • 6
    Digitale Medien
    Digitale Medien
    Conduction processes of the gramicidin channel (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 385-399 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The significance of the gramicidin channel, its structural elements, and the importance of the peptide libration mechanism are reviewed. Elemental ionic processes of the single-channel currents are considered, which indicate the possibility of two- and three-site models. Data are presented which demonstrate the absence of interactions required for the three-site model, and the resulting free-energy profile for the two-site model is given for the most probable conducting state. The need to extend analyses to include an understanding of multiple conformational states is outlined, and results from approximate conformational energy calculations are presented showing that there are numerous low-energy conformations for the side chains of gramicidin. Specifically the interactions between L·Trp9 and L·Trp15 side chains and between D·Leu4…D·Leu10 are analyzed to show the existence of several energy minima separated by appreciable barriers. These findings provide the basis for understanding facilitated entry of the second ion into the channel and the occurrence of lipid-dependent dispersion of conductance states. Finally perspectives of the molecular mechanism of anesthetics are discussed relevant to the gramicidin channel mean lifetime and single-channel currents.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560200735
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  • 7
    Digitale Medien
    Digitale Medien
    Determination of the possible conformations of the residues linked in a polypeptide chain (1965)
    New York : Wiley-Blackwell
    Biopolymers 3 (1965), S. 591-592 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1965.360030510
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  • 8
    Digitale Medien
    Digitale Medien
    Stereochemical criteria for polypeptides and proteins. V. Conformation of a system of three linked peptide unitsContribution No. 236 from the Center of Advanced Study in Physics, University of Madras, India. (1968)
    New York : Wiley-Blackwell
    Biopolymers 6 (1968), S. 1425-1436 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The general conformations of a system of three linked peptide units are studied, and it is found that there are three types of conformations which contain NH…O hydrogen bonding between the first and the third units. One of them is part of a 310-helix, while the other two arc nonhelical. The two nonhelical conformations are very similar, and in both the cases the peptide chain turns around, reversing the direction of progress. Such a conformation can therefore occur in the region where a polypeptide chain folds back on itself, as in the cross-β structure. The method of representing these interesting tripeptide conformations in a (φ,ψ) map is described. Examples of such hydrogen-bonded, nonhelical conformations which occur in peptides and proteins are discussed - e.g., in cyclohexaglyeyl, an open tetrapeptide Gly-L-Pro-L-Leu-Gly, and in parts of the lysozyme chain.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1968.360061006
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  • 9
    Digitale Medien
    Digitale Medien
    Synthesis, characterization, and solution properties of 5-ethyl-substituted poly(L-prolines). Synthesis of cis- and trans-5-ethyl-L-proline and optically active poly(cis-5-ethyl-D-proline) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 1643-1656 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This article reports a continuation of our work on the substituent effects on the preferred helical conformations and the mutarotation of substituted poly(L-prolines). The size of the substituent has been increased from a methyl group to an ethyl group in the 5 position. The purpose is twofold: (i) according to our theoretical conformational energy calculations, an ethyl group in the 5 position can exert a greater steric effect than can a methyl group; and (ii) the rotation-isomerization of the ethyl group introduces a new intriguing fact to the problem. The cis isomer of 5-ethylproline was synthesized by catalytic hydrogenation of Δ′-2-ethylpyrroline-5-carboxylic acid, whereas for trans-5-ethylproline, a chemical separation method involving p-toluenesulfonyl chloride was used. The resolution of cis-5-ethylproline and the assignment of absolute configurations have been carried out by fractional crystallization and circular dichroism spectroscopic techniques, respectively. Poly(cis-5-ethyl-D-proline) was obtained from its corresponding N-carboxyanhydrides via a ring opening polymerization.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.170210607
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  • 10
    Digitale Medien
    Digitale Medien
    Conformational studies of poly(cis-5-ethyl-D-proline) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 1751-1761 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two possible conformations for poly(cis-5-ethyl-D-proline) have been identified and characterized by using combinations of 1H- and 13C-NMR, CD, and ORD spectroscopic techniques. Both forms have helical conformations similar to those of poly(L-proline) characterized by different amide bonds (cis and trans). However, the carbonyl group of the amide in poly(cis-5-ethyl-D-proline) form II (trans) seems to be closer to perpendicular orientation with respect to the helical axis than in poly(L-proline) form II. The pyrrolidine ring conformation of form I (cis) is probably β+γ--puckered, whereas for form II it is probably β+-puckered in nature. The side-chain ethyl groups prefer to adopt anti conformations to the C5—H bond, or prefer to have χ = 180°, regardless which of the two forms poly(cis-5-ethyl-D-proline) may like to assume. The experimental results agree well with our previous theoretical conformational energy calculations.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1983.170210617
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