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  • Articles  (7,318)
  • Wiley-Blackwell  (7,318)
  • 1975-1979  (7,318)
  • 1970-1974
  • 1978  (7,318)
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  • 1975-1979  (7,318)
  • 1970-1974
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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have tested 21 different basis sets of synthetic DNA circular dichroism spectra and have slected one for use in spectral analyses of natural DNAs. This “standard” set consists of spectra of eight polymers: poly[d(A-A-T)·d(A-T-T)], poly[d(A-G-G)·d(C-C-T)], poly[d(A-T)·d(A-T)], poly[d(G-C)·d(G-C)], poly[d(A-G)·d(C-T)], poly[d(A-C)·d(G-T)], poly[d(A-T-C)·d(G-A-T)], and poly[d(A-G-C)·d(G-C-T)]. This basis set, applied according to the first-neighbor polymer procedure of Gray and Tinoco, allows a more uniformly accurate spectral analysis of six natural complex DNAs and eight (A+T)-rich satellite DNAs for base composition and first-neighbor frequencies than was previously possible. We find that spectra of poly[d(A)·d(T)] and/or poly[d(A-C-T-)·d(A-G-T)] are not generally required for good analysis results but we show in this and the following paper that these spectra are needed for the most accurate analyses of some satellite DNAs.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of counterions with a suitably long, charged oligomer appears susceptible to treatment in the context of polyelectrolyte theory by the introduction of an end-effect parameter that reflects the reduced association of counterions with the terminal regions of the oligo-ion. Use of a physically reasonable value for the end-effect parameter provides excellent agreement between theory and the experimental data of Elson, Scheffler, and Baldwin [J. Mol. Biol. 54, 401-415 (1970)] on the dependences of melting temperature on salt concentration and chain length for a series of hairpin helices formed by d(TA) oligomers. The differences in behavior expected for hairpin, dimer, and oligomer-polymer helices are discussed. The salt dependence of the end-joining equilibrium investigated for λ DNA by Wang and Davidson [Cold Spring Harbor Symp. Quant. Biol. 33, 409-415 (1968)] is treated as an oligomer-polymer interconversion. The dependence of equilibrium constant for this reaction on counterion concentration is in good agreement with that predicted by theory for an end-region totalling 24 nucleotides, the known length of the λ ends.
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent denaturation is developed along thermodynamic lines rather than from multiple-binding theory. Almost all the relations derivable from site-binding theory have their counterparts in the thermodynamic formulation showing that the details of binding models may be sufficient but are not necessary for the general description of solvent denaturation. Equations are derived for the effect of denaturant concentration on stability at constant temperature and on tm. It is recommended that the thermodynamic treatment be used instead of binding models unless stoichiometric interactions are demonstrable experimentally.
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1361-1372 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical properties of the 1,N6 - etheno derivative of ApA (εApεA) have been studied. Absorbance and CD measurements suggest that (1) neutral salts tend to unstack this molecule and (2) the stacking interaction is weaker than in ApA. εApεA is found to be quenched strongly with respect to the monomer. (εAMP); this quenching is solvent dependent (1M NaCl 〉 5M NaClo4〉40%glycerol) and increases with the ratio of temperature to viscosity (T/η) in each case. Fluorescence lifetime measurements also reveal a temperature- and solvent-dependent decay which is nonlinear on a semilog plot. In the presence of 95% glycerol, this decay return to linearity. These data have been considered from two points of view: (1) two-state pictures which are based on thermodynamic least-squares fit to quatum yield and CD curves, together with two exponential fits to the decay curves and (2) a dynamical model in which relatives fluorophore motion leads to deexcitation via intramolecular collision. A simple model of type (2) gives qualitative agreement with the observed behavior.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1385-1386 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1513-1521 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The native antibiotic polymyxin B, carrying five positive charges, displaces the monoacetylated on from its adsorbed state at the interface between negatively charged lipid layers ans water. A simulation model for asdorption, governed by electrostatic forces, is presented. The model adequently representes the competitive adsorption kinetics and equilibria.
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  • 8
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study the role of D-amino acid residues in keeping the stable β-sheet conformation and in the antimicrobial activity of gramicidin S (GS), the four analogs of GS containing D-Ala, L-Ala, Gly, and Aib (α-aminoisobutyric acid) in place of D-Phe were synthesized. D-Ala-and Gly-containing analogs showed antimicrobial activity, while those containing L-Ala and Aib showed no activity. Conformation of these analogs and their derivatives were studied by comparison of ORD and CD spectra and by slective methylation method. It is concluded that the biologically active analogs have β-sheet conformation while inactive analogs have a much different conformation from that of GS. This indicates that D-Ala-Pro and Gly-Pro sequences favor taking a β-bend form but L-Ala-Pro and Aib-Pro sequences do not because the presence of L-side methyl group on the α-carbon atom of LAla and Aib residues destabilizes the β-bend form. This would explain why the inactive analogs which take a different conformation from that of the active ones result in the loss of activity.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 811-814 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 843-855 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Earlier studies by the authors showed that the collagen fibrils in rat-tail tendon have a bi-modal distribution of fibril diameters from a time shortly after birth through to the onset of maturity at about 3-4 months. Present work has extended those observations for rats up to the age of 2 years. Histograms of the fibril diameter distributions for mature tail tendon and direct electron microscope observations show that the fibrils break down as the tendon ages. Further work on the constant diameter subfibrils of diameter 140 Å described previously, has confirmed that these are part of the elastic fibers present in tendon at all ages. It has been shown that there is relatively little variation in the collagen fibril diameter distribution as a function of the position of the specimen in the tail, and as the measured percentage of the area taken by the collagen fibrils present at any particular point. Estimation of the fibrillar collagen content of rat-tail tendon as a function of age indicates that it increases steadily from birth and reaches a maximum at the onset of maturity, beyond which the fibrillar collagen content appears to remain constant.
    Additional Material: 6 Ill.
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