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  • Wiley-Blackwell  (18,601)
  • American Institute of Physics  (12,791)
  • 1985-1989  (16,966)
  • 1980-1984  (14,426)
  • 1925-1929
  • 1986  (16,966)
  • 1983  (14,426)
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  • 1985-1989  (16,966)
  • 1980-1984  (14,426)
  • 1925-1929
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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 2
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 15-25 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular theory of protein secondary structure is presented that takes account of both local interactions inside each chain region and long-range interactions between different regions, incorporating all these interactions in a single Ising-like model. Local interactions are evaluated from the stereochemical theory describing the relative stabilities of α- and β-structures for different residues in synthetic polypeptides, while long-range effects are approximated by the interaction of each chain region with the averaged hydrophobic template. Based on this theory, an algorithm of protein secondary structure prediction is proposed and examples are given of “blind” predictions made before the x-ray structural data became available.
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  • 3
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 27-31 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To increase our understanding of peptide-water interactions, we are simulating the behavior of water molecules in the intermolecular channels of [Phe4Val6]antamanide dododecahydrate crystals. There is good overall agreement between the positions predicted using two alternative potential functions and those that have been observed by x-ray diffraction. Detailed differences between the predictions for the two potential functions are discussed.
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  • 4
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    Biopolymers 22 (1983), S. 49-58 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental measurements of disulfide bond stability at various stages of protein folding are considered in terms of the effective concentrations of the thiol groups relative to each other; values of up to 107M are observed, so that intramolecular interactions within the interior of a protein are much more stable, and provide greater stability to the folded conformation, than those on the surface or in a flexible segment. Intramolecular interactions can have substantially lower free energies than intermolecular, for solely entropic reasons; this implies that polar interactions, such as hydrogen bonds and salt bridges, can provide net stabilization to a folded conformation, in spite of the unfolded protein having intermolecular interactions with the solvent. These considerations can account for the lower free energy and enthalpy of the folded state and are useful for considering protein flexibility.
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  • 5
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    Biopolymers 22 (1983), S. 87-91 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Near- and far-uv CD spectra of microtubule protein preparations have been examined to study the possible role of protein conformation in relation to the kinetics of the self-assembly of these proteins into microtubules in vitro. Although tubulin can form conformations with high helical content under apolar solution conditions, this transformation is apparently not involved in self-assembly. There is no major perturbation of tubulin near-uv CD by reagents and solution conditions favoring assembly. Thus, in these preparations, tubulin, as dimer and as oligomer with MAPs, is effectively in the conformation in which it undergoes self-assembly. This conclusion is consistent with a hybrid model of assembly of microtubule protein involving direct incorporation of oligomeric species as an alternative to the condensation polymerization of tubulin dimer as the exclusive assembly mechanism.
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  • 6
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 101-105 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand-modulated kinetics of the autoproteolysis of thermolysin and the high-molecular-weight products of the reaction provide evidence for the conclusion that separation of the two structural domains is most probably the first step on the unfolding pathway of the protein under native conditions.
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  • 7
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    Biopolymers 22 (1983), S. 125-129 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The in vivo pathway of folding and subunit assembly of a trimeric bacteriophage protein has been studied by characterizing precursors to the native protein and by analyzing temperature-sensitive mutations that kinetically block the pathway. The native trimer is formed via an intermediate composed of three partially folded chains, the protrimer. At 39°C, temperature-sensitive mutations prevent the formation of both the native trimer and the protrimer, possibly by destabilizing earlier intermediates. However, the mutations do not affect the stability of the native protein, formed at 30°C. Thus, these mutations identify amino acid residues involved in interactions that determine the folding pathway.
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  • 8
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    Biopolymers 22 (1983), S. 1677-1696 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the kinetics of O2 release by oxyhemoglobin caused by sodium dithionite, in the presence and in the absence of organic cosolvents (monohydric alcohols and formamide) at 10°C. This study was performed by using standard stopped-flow techniques coupled with microprocessor-based data acquisition. We have fitted the experimental data to a mathematical expression obtained on the basis of a two-state model that takes into account the kinetic heterogeneity between α- and β-chains and the presence of αβ-dimers in oxyhemoglobin solutions. Results indicate that the cosolvents mainly affect the allosteric parameter L, i.e., the T ⇄ R conformational equilibrium of hemoglobin, leaving the intrinsic deoxygenation rates of both R and T states almost unaltered. The L values obtained in the present work are in excellent agreement with analogous values previously estimated from oxygen equilibrium measurements.
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  • 9
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    Biopolymers 22 (1983), S. 1657-1675 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Porcine submaxillary mucin (PSM) is a glycoprotein composed of a protein core and frequent, short oligosaccharide side chains. We report static and dynamic light scattering experiments and intrinsic viscosities for PSM in aqueous solvent systems. In 0.1M NaCl solution, the data suggest PSM exists as large, internally branched, highly hydrated, polydisperse aggregates that slowly dissociate to give a stable species of weight-average molecular weight (Mw) 7.4 × 106. In 6M GdnHCl solution, the noncovalent bonds between PSM molecules are broken, giving a highly elongated molecule of Mw = 2.0 × 106. The irreversible nature of this dissociation suggests that the forces that stabilize the native aggregates of PSM in 0.1M NaCl are specific in nature. On reduction of PSM with mercaptoethanol, the polydispersity decreases and Mw also decreases to 9 × 105. A discrete change is observed in the solution properties of PSM in 0.1M NaCl at a concentration of 2mg/mL, manifested by a sudden decrease in the translational diffusion coefficient, an increase in viscosity number, and a decrease in slope of the osmotic compressibility. We tentatively propose that a weak and reversible secondary association process occurs at this concentration, although a purely hydrodynamic interaction cannot be ruled out.
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The uv linear dichroism of calf thylus DNA has been studied at different degrees of orientation both in flow-oriented ethanol-water solutions and in a stretched aqueous host of poly(vinyl alcohol) (PVA). The reduced dichroism (LDR) curves in the region 250-290 nm for DNA in PVA films at 75 and 100% relative humidity (r.h.) are in fair agreement with the curves calculated for the A- and B-forms of DNA, based on the fiber structures and the π-π* transitions of the free bases. This suggests that DNA adopts its A and B conformations in PVA at 75 and 100% r.h. In ethanol, on the other hand, a deviation from the A-form spectrum shows that the conformation of DNA in the solution can differ from the fiber structure. At shorter wavelenghts, a positive contribution to LDR is explained in terms of an out-of-plane polarized n-π* transition.
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  • 11
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    Biopolymers 22 (1983), S. 1759-1767 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A vibrational analysis has been performed for a double-helix-single-strand junction. A Green's function technique has been used in treating the junction as a defect on an otherwise perfect system of infinite chain homopolymers. We calculate that the hydrogen-bond stretching at the junction is amplified by a factor of two relative to the interior of the double helix, B poly(dG)-poly(dC). Breathing modes localized near the junction have also been predicted at 77 and 94 wave numbers. The calculated results are shown to be consistent with predictions from recent nmr studies.
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  • 12
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 13
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nmr studies of the protected and free tetrapeptide Gly-Pro-Gly-Gly were carried out in β-turn-supporting solvents, that is, in CDCl3 for Z-Gly-Pro-Gly-Gly-OMe and in Me2SO-d6 for H-Gly-Pro-Gly-Gly-OH. Comparisons with specifically α-deuterated analogs gave complete assignments of the NH and methylene regions. Analysis of chemical shifts, coupling constants, and the temperature dependence of chemical shifts show that the peptide adopts a type II β-turn conformation. This turn is stabilized for the protected tetrapeptide by two hydrogen bonds between (i) C=O (Gly1) and NH(Gly4), and (ii) urethane function NH and methyl ester C=O.
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  • 14
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio minimal and split-valence basis set calculations have been performed on compounds that are involved in retro-inverso modifications, i.e., gem-diaminoalkyl and malonyl structures. These calculations are compared with empirical force field calculations and the minor differences discussed. All calculations agree that the preferred helical conformation of the isolated gem-diaminoalkyl and malonyl derivatives of residues found in the retro-inverso modified peptides is 5-8 kcal/mol lower than the Ceq7 conformation preferred by the isolated peptide residues. Population analysis and contour plots of the charge distribution are used to help explain the differences between the model compounds.
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  • 15
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 17
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    Biopolymers 22 (1983), S. 1449-1460 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: SCF-LCAO-MO ab initio calculations were carried out for the interaction between a charged amino acid and a water molecule. The results obtained were fitted by an analytical potential function of the atom-atom type, and the corresponding potential surfaces were examined by means of orientationally optimized isoenergy contour maps. Monte Carlo simulations were also carried out on a few selected solute-water clusters at T = 300 K, in order to obtain insight into the solvation structure.
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  • 18
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved cube method has been developed for calculating the intensity of diffuse x-ray scattering of macromolecules in solution using a certain set of their atomic coordinates. The technique is based on the ideas of B. Lee and F. M. Richards [(1971) J. Mol. Biol. 55, 374-400] and Richards [(1977) Annu. Rev. Biophys. Bioeng. 6, 151-176] on the possibility of estimating the molecular and accessible surface of a particle by “rolling” a sphere, simulating a water molecule, on its molecular surface. It is shown that this technique is more advantageous than earlier versions of the cube methods. The improved technique for calculating scattering curves was utilized for several globular proteins, and for the first time, reliable scattering curves were obtained for protein-“bound” water complexes. In the case of globular proteins and tRNA, this technique has permitted a strict evaluation of their accessible surfaces, their volumes, and, apparently for the first time, their complete molecular surfaces.
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  • 19
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 20
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    Biopolymers 22 (1983), S. 2501-2506 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
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    Biopolymers 22 (1983), S. 2523-2538 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extended retro-inverso modification was introduced at the central six residues of the somatostatin molecule, the region of internal enzymatic degradations. The synthesis of the analog [Ala4,g-Phe6-r-D-Phe7-r-D-Trp8-r-D-Lys9-r-D-Thr10-m-R,S-Phe11]-somatostatin required a unique strategy accommodating the unusual structure. Side-chain protection based on the t-butyl group in combination with Fmoc and Nps α-amino protection was employed. The key component containing the gem-diaminoalkyl residue was generated by an iodobenzene bistrifluoroacetate-mediated reaction. The separation of diastereomers of the cyclic tetradecapeptide in highly pure form was accomplished by high-performance liguid chromatography on a semipreparative scale. The analogs exhibited very low potency in the growth hormone inhibition test in vitro. This is interpreted as the consequence of the complex structural changes created by the extended retro-inverso modification.
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  • 22
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of internal and overall motions in native (double-stranded) and denatured (single-stranded) DNA fragments 120-160 base pairs (bp) long is examined by molecular-dynamics modeling using 13C-nmr spin-relaxation data obtained over the frequency range of 37-125 MHz. The broad range of 13C frequencies is required to differentiate among various models. Relatively narrow linewidths, large nuclear Overhauser enhancements (NOEs), and short T1 values all vary significantly with frequency and indicate the presence of rapid, restricted internal motions on the nanosecond time scale. For double-stranded DNA monomer fragments (147 bp, 24 Å diam at 32°C), the overall motion is that of an axially symmetric cylinder (τx = ∼10-6 s;τZ = ∼1.8 × 10-8s), which is in good agreement with values calculated from hydrodynamic theory (τx = ∼1.8 × 10-6 s; τZ = ∼2.7 × 10-8 s). The DNA internal motion can be modeled as restricted amplitude internal diffusion of individual C—H vectors of deoxyribose methine carbons C1′, C3′, and C4′, either with conic boundary conditions (τw = ∼4 × 10-9 s, θcone = ∼21°) or as a bistable jump (τA = τB = ∼2 × 10-9 s, θ = ∼15°). We discuss the critical role in molecular-dynamics modeling played by the angle (β) that individual C—H vectors make with the long axis of the DNA helix. Heat denaturation brings about increases in both the rate and amplitude of the internal motion (described by the wobble model with τW = ∼0.2 × 10-9 s, θcone = ∼50°), and overall motion is affected by becoming essentially isotropic (τx = τZ = ∼5 × 10-8 s) for the single-stranded molecules. Since 13C-nmr data obtained at various DNA concentrations for C2′ of the deoxyribose ring is not described well by the above models, a new model incorporating an additional internal motion is proposed to take into account the rapid, extensive, and weakly coupled motion of C2′.
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  • 23
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of methyl orange with poly(L-lysine) was studied kinetically by the stopped-flow technique with CD detection, as well as by static CD titration experiments. In the static experiments, the differences observed in the polymer-to-dye ratio dependences of the CD spectra and absorption spectra suggested at least two kinds of bound states of the methyl orange attached to the polymer. The kinetic experiments using the stopped-flow apparatus, however, revealed four distinct reaction processes. The reaction mechanism was elucidated from the concentration dependence of the time constant for each process as follows: the first process was attributed to the bimolecular binding step of methyl orange to the side chain of poly(L-lysine), the second and third process were ascribed to the intramolecular reaction of the polymer-dye complex, and the fourth process was found to be the intermolecular aggregation of the polymer-dye complex. The origin of the stacking of methyl orange on poly(L-lysine) is discussed on the basis of the characteristics of signal amplitudes obtained from the kinetic experiments for these processes.
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  • 24
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel devices for the spectroscopic and chromatographic analysis of the denaturation curves of the protein are described. A multidimensional spectroscopic measuring system makes it possible to carry out simultaneous and continuous acquisition of a set of data of different spectroscopic dimensions at several wavelengths in the course of increasing or decreasing denaturational perturbation. GuHCl-gradient chromatography can provide information about the progressive change of the protein volume in the course of increasing GuHCl concentration. Thus, denaturation curves with a high data-point density can be obtained. The data-storing function by a magnetic disk memory provides enough precision for a rigorous investigation of the correlation among the curves that probe different aspects of denaturation. The GuHCl denaturation of RNase A, cytochrome c, and pepsinogen are studied to demonstrate the high performance of these devices. Three types of transitions are found in these three proteins and the multiphasic nature of the transitions is clearly detected in the last two proteins.
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  • 25
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 26
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    Biopolymers 22 (1983), S. 2169-2172 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 27
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    Biopolymers 22 (1983), S. 2207-2217 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A sufficiently long semiflexible filamentous macromolecule is theroretically expected to exhibit three different domains of behavior of its apparent diffusion coefficient Dapp(K) as a function of scattering vector K: (1) the small wave vector limit, where Dapp(K) = D0 is the translational diffusion coefficient of the center-of-mass; (2) the universal K3 region, where Dapp(K) = (kBT/6πη)K is a universal function of K independent of any property of the molecule itself; (c) the plateau region at large K2, where Dapp(K) approaches either a plateau, or gradually sloping quasiplateau, characteristic of local (elastic) rigid-body motions of the filament. The existence of each of these different domains has now been established experimentally for at least some polymers. The boundaries of the universal K3 region and the plateau region are determined theoretically here using precise quantitative criteria for universal or plateau behavior of Dapp(K) for a Rouse-Zimm model containing N + 1 subchains with rms subchain extension b. Allowing a maximum of 13% nonuniversal behavior, the domain of the universal K3 region is given by K2R2G = K2Nb2/6 ≥ 7 and K2b2 ≤ 0.54. Allowing as much as 10% nonplateau behavior, the boundary for onset of plateau behavior is K2b2 = 18.3. Dapp(K) is at least 50% nonuniversal when K2b2/6 = 6 ln 3. Extension of these results to DNA is examined theoretically, and good agreement of the pertinent predictions with published experimental data is demonstrated.It is concluded that no truly universal K3 region exists for DNA with Mr ≤ 107 and persistence length a ≥ 450 Å, although marginally (≤17% nonuniversal) universal behavior, is exhibited in a very narrow domain 0.64 × 1010 ≤ K2 ≤ 0.84 × 1010 cm-2 for φ29 DNA (Mr = 11.5 × 106). More than 50% of Dapp(K) is governed by local (elastic) rigid-body motions when K2 = 5.23 × 1010 cm-2. The existence of a very wide region of nonuniversal apparent K3 behavior extending up to very large K2, far into the plateau region, is demonstrated in a plot of Dapp(K)/K vs K2 for the Rouse-Zimm model. This is shown to stem in part from visual artifacts of plotting Dapp(K)/K vs K2, even for rigid species.
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  • 28
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    Biopolymers 22 (1983) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 29
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    Biopolymers 22 (1983), S. 2353-2366 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational relaxation tiem τ3 of DNA molecules (Mw ≃ 5 × 106) in solution has been determined by the transient electric birefringence method. The analysis of the birefringence decay makes it possible to study only the higher-molecular-weight fraction, the molecules being considered as rigid elongated particles in a short time scale. A marked concentration dependence of the relaxation time has been observed for DNA in low ionic strengths. Above a critical concentration c*, τ3 increases with the DNA concentration, c. The value of c* increases with the ionic strength. For 10-3 ionic strength (with NaCl), c* is about 10 μg/mL; then we observe the same strong concentration dependence of rotational relaxation times as recently reported for rodlike M-13 viruses [Maguire, J. F., McTague, J. P. & Rondelez, F. (1980) Phys. Rev. Lett. 45, 1891-1894]. These results may be discussed in terms of the Doi-Edwards theory for rotational relaxation time of rigid macromolecules [Doi, M. (1975) J. Phys. 36, 607-611; Doi, M. & Edwards, S. F. (1978) J. Chem. Soc. Faraday Trans. 74, 918-932] and the critical concentration above which the interactions between the molecules begin to appear allows determining the corresponding molecular length. We observe a very good agreement between the DNA lengths obtained from the c* values and by using the infinite dilution value of τ3 and Broersma's equation. Therefore, only highly diluted solutions can be used if intrinsic molecular properties based on the rotational diffusion of high-molecular-weight elongated molecules are studied.
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  • 30
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    Biopolymers 22 (1983), S. 2411-2421 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A thermodynamic treatment of the helix-coil transition of synthetic polypeptides in binary organic solvent mixtures is extended to describe isobaric heat-capacity increments associated with the phenomenon. This development resolves such increments into three components: two associated respectively with intrinsic differences between the ordered and disordered states of the macromolecule and between the coil-solvent complex and its components, and a third term derived from the temperature dependence in the fraction of coil residues bound to active solvent. Insights derived from this analysis are also applied to the discussion of some heat capacity increments associated with the denaturation of globular proteins.
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  • 31
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    Biopolymers 22 (1983) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 32
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    Biopolymers 22 (1983), S. 2507-2511 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
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    Biopolymers 22 (1983), S. 2539-2547 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the humidity-sensitive spacing, d, related to the lateral packing of collagen molecules was measured for fully hydrated collagen. In the vicinity of 0°C, a sudden change in d was observed, which was reversible with temperature. In the diffraction profile, below 0°C, a set of diffraction peaks identified with the hexagonal crystalline form of ice was observed. With the reduction in water content, the intensity of the set of diffraction peaks decreased and was found to be zero at a water content of 0.38 g/g collagen. These results were considered to be caused by the frozen water in collagen fibril below 0°C. According to the water content dependence of d, it was considered that up to a certain water content water absorbed would be stowed in the intermolecular space of collagen and above that water content water molecules would aggregate to make pools, i. e., extrafibrillar spaces. The unfreezable bound water was considered to be located in the intermolecular space of collagen. Size of the extrafibrillar space, determined from the intensity analysis of a smallangle x-ray scattering pattern, corroborates the speculation that the water showed in the extrafibrillar space is freezable and free. The formation of the hexagonal crystalline form of ice in the extrafibrillar space was considered to cause the sudden change in d at 0°C.
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    Biopolymers 25 (1986), S. 1-4 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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  • 35
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    Biopolymers 25 (1986), S. 17-30 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mononucleotide conformations are important in understanding the structural aspects of nucleic acids and polynucleotides. In order to study the influence of stacking interactions between adjacent bases in a polynucleotide on the preferred conformations of mononucleotides, conformational energy calculations have been carried out on dinucleoside monophosphate fragments. Four base sequences - d(ApT), d(TpA), d(CpG), and d(GpC) -  have been analyzed in the framework of helical structures. Flexibility of the furanose ring has been incorporated in the investigations. Energetically favored conformers of the four compounds correspond to a variety of left- and right-handed uniform helical structures, similar to those of the commonly observed polymorphous forms. Implications of these investigations on the further understanding of double-helical polynucleotide conformations are briefly discussed.
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  • 36
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    Topics: Chemistry and Pharmacology
    Notes: We have measured vibrational CD spectra in the 3600-1250 cm-1 region of two monodisperse, protected octapeptides, which form right-handed 310-helices in CDC13 solution. The spectra are similar in sign pattern to those obtained for right-handed α-helices in solution but are smaller in magnitude and, additionally, provide evidence of some line-shape differences. The delineation of this type of ordered conformation was accomplished by means of 1H-nmr. Such a solution structure is consistent with the x-ray crystal structure of one of these molecules.
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  • 37
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    Biopolymers 25 (1986), S. 135-152 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of a series of biologically active gastrin fragments with calcium ions has been investigated by CD in trifluoroethanol. It was found that the gastrin octapeptide pGlu10,Nle15-HG[10-17] binds one calcium ion per molecule. The hypothesis is made that the binding involves the C-terminal, biologically important tetrapeptide. When the chain is elongated to the gastrin nonamer pGlu9,Nle15-HG[9-17], a second binding site is available, which is most likely situated at the N-terminal part of the molecule. Further elongation of the peptide chain up to the dodecapeptide pGlu6,Nle15-HG[6-17] does not provide any additional binding site. Saturation of the two sites in the shorter peptides produces different changes in the chiroptical properties in the near- and far-uv. As the chain is elongated, this difference tends to disappear. This result is consistent with an increased conformational order of the longer peptides. In the shorter fragments, the strength of this second binding is appreciably lower than that of the first, while in the longer peptides, the strength of the two bindings is comparable. On the assumption that the variation of the CD properties is proportional to the extent of binding, the constant for the binding of the second ion was determined to be of the order of 5 × 105 L/mol for the nonapeptide.
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    Biopolymers 25 (1986) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 39
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  • 40
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  • 41
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    Biopolymers 25 (1986), S. 249-266 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present molecular mechanical calculations on the complexes of netropsin with dA6·dT6, d(TATATA)2, d(CGCGCG)2, and d(CGCGAATTCGCG)2. The complexes were model built using computer graphics and then completely energy refined. Our calculations are consistent with the observed AT preference for netropsin and suggest that mixed sugar pucker geometries should be more stable than uniform in netropsin complexes with poly[d(A-T)]·poly[d(A-T)] and poly(dA)·poly(dt). The netropsin·d(TATATA) and netropsin·dA6·dT6 complexes are significantly different in structure, leading to a possible reason why the observed thermodynamics of netropsin-association with poly[d(A-T)]·poly[d(A-T)] and with poly(dA)·poly(dT) are so different. We also model built and energy refined a structure of netropsin-d(CGCGAATTCGCG)2 using as a guide the nmr data of Patel [(1982) Proc. Natl. Acad. Sci. USA, 79, 6424-6428] and found a three-dimensional structure qualitatively consistent with the NOE enhancements observed by him. After our calculations were completed, we learned of an x-ray structure of a netropsin:d(CGCGAATTCGCG)2 complex, and we compared the structure found in our calculation with the x-ray structure.
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  • 42
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    Topics: Chemistry and Pharmacology
    Notes: We utilize the dynamic quenching of the triplet state of methylene blue by molecular oxygen to observe changes in the rate at which oxygen can penetrate the helix as a function of base-pair composition. The results indicate that the interior of the oligonucleotide dA-dT is more accessible than dG-dC to small molecules such as dioxygen.
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    Biopolymers 25 (1986) 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Biopolymers 25 (1986), S. 375-392 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of spermine with nucleic acids is simulated theoretically using refined semi-empirical energy formulae and an advanced minimization procedure. Various nucleic acids are considered: model homopolymeric DNA's, a dodecamer (CGCGAATTCGCG) of type B-DNA, as well as a transfer RNA, tRNAPhe. The dominant role of electrostatic potential in determining the preferential binding sites of spermine is demonstrated in each of these cases and the role of counterions, nucleic acid structure, and base-pair sequence is analyzed.
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    Biopolymers 25 (1986), S. 241-247 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Permittivity ε′ and dielectric loss ε″ of aqueous Na-DNA gels have been measured at 10 GHz in the temperature interval -15 to + 45°C. The experimental results are analyzed in terms of a three-component equation (Na-DNA, interfacial water, bulk water) and yield a value of 35 water molecules/nucleotide interacting with DNA. According to theoretical and experimental data the presence of strongly bonded and weakly bonded water is considered. The modified water exhibits a mean dielectric relaxation time two-or threefold greater than that of bulk water.
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    Biopolymers 25 (1986), S. 291-306 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of solvent viscosity (ηs) and temperature (T) on the shape of the concentration dependence of the principal and total recoils in creep-recovery viscoelastometry experiments has been studied for T4 DNA solutions. The range of DNA concentration (c) was 2 - 40 μg/ml; glycerol, 70-80% v/v, sucrose, 60% v/v; NaCl, 5 mM - 1M; and T, 275 - 323 K. A linear proportionality between recoil and c was obtained at high ηs/T. At low ηs/T, the c-dependence was nonlinear, approaching saturation at higher c. At low c, the slope of both curves was the same. Transition between “linear” and “nonlinear” values occurred over a narrow range of ηs/T (a width of 1-5 K if ηs/T was changed by varying T). (ηs/T)tr, the midpoint of the transition, was independent of solvent properties other than viscosity. Also, (ηs/T)tr increased with c. For a given c, ηs/T values above this transitional value yield linear behavior; below this, nonlinear behavior. The ratio of linear to nonlinear recoil values is a linear function of c with Kc, the slope of this dependence, independent of ηs and T. A kinetic model for the observed nonlinearity of recoil with c is presented. It explains the independence of Kc on ηs and T. An attempt has been made to explain the linear-nonlinear transitions by comparison of τ1 and TR, the lifetime of the contact points of the polymer network in the de Gennes theory. The nonlinear values are consistent with a pseudogel that exists when τ1 〈 TR. At τ1 〉 TR, the DNA behavior is similar to that in dilute solutions (linear values). Thus, the condition for transition is τ1 = TR. However, some unsolved problems remain.
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    Biopolymers 25 (1986), S. 337-350 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If protein single crystals larger than those suitable for x-ray analysis are obtained, various spectroscopic, thermal, mechanical, and electrical measurements become possible. To understand the factors governing the crystal size, tetragonal lysozyme crystals were grown in batches at 15°C from solutions of different protein and salt concentrations between pH 4-7. The number and size of the crystals, and the protein concentration remaining in the supernatant, varied markedly with the initial salt amount, pH, and cation species, but large crystals always grew when the initial protein concentration (P) was in a narrow range of 2.5-3 times the crystal solubility (S). It was also shown (1) that the period before the first crystals appeared (D) varied as D ∝ (P/S)-n, where n ≃ 5, and (2) that many previous experiments used more supersaturated solutions than the optimal ones thus determined. The reason why large crystals grow only from moderately supersaturated solutions is discussed. The crystal size of the orthorhombic form grown at 40°C was less sensitive to pH and P than the tetragonal form. An effort to measure D and the solubility at 40°C revealed many differences between the two crystal forms, which we ascribe to different interactions to promote crystallization.
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    Biopolymers 25 (1986), S. 393-405 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pinellin is a plant protein extracted from the rhizome of the Chinese herb Pinellia. It has the ability to abort early pregnancy in mice as well as in rabbits. Studies on the conformational changes of pinellin have been carried out in our laboratory using intrinsic fluorescence and CD. Experimental results show that some tryptophanyl side chains are buried more deeply than others, which results in the heterogeneity of tryptophanyl emission. CD data indicated a high content of β-pleated sheet and β-turn for the backbone conformation. The results of fluorescence and CD measurements both demonstrated the presence of intermediates along the path of denaturation. The following was proposed as the unfolding mechanism of pinellin in 6M guanidine hydrochloride: native state → first intermediate → second intermediate → fully unfolded state.
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    Biopolymers 25 (1986), S. 469-487 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourier transform ir (FTIR) spectra of 21 globular proteins have been obtained at 2 cm-1 resolution from 1600 to 1700 cm-1 in deuterium oxide solution. Fourier self-deconvolution was applied to all spectra, revealing that the amide I band of each protein except casein consists of six to nine components. The components are observed at 11 well-defined frequencies, although all proteins do not exhibit components at every characteristic frequency. The root mean square (RMS) deviation of 124 individual values from the 11 average characteristic frequencies is 1.9 cm-1. The observed components are assigned to helical segments, extended beta-segments, unordered segments, and turns. Segments with similar structures do not necessarily exhibit band components with identical frequencies. For instance, the lower frequency beta-structure band can vary within a range of approximately 15 cm-1. The relative areas of the individual components of the deconvolved spectra were determined by a Gauss-Newton, iterative curve-fitting procedure that assumed Gaussian band envelopes for the deconvolved components. The measured areas were used to estimate the percentage of helix and beta-structure for each of 21 globular proteins. The results are in good general agreement with values derived from x-ray data by Levitt and Greer. The RMS deviation between 22 values (alpha- and beta-content of 11 beta-rich proteins measured by both techniques) is 2.5 percentage points; the maximum absolute deviation is 4 percentage points.
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    Topics: Chemistry and Pharmacology
    Notes: A time-resolved fluorescence study of ethidium bromide (EB) in the presence of poly(dG-dC) and of poly(dG-dC) modified by chlorodiethylenetriamine platinum(II) chloride is presented under solvent conditions in which these polymers adopt the Z-conformation (high ionic strength). It is shown that these polynucleotides can intercalate a very small quantity of EB. The binding parameters have been determined. The fluorescence lifetime of EB is slightly higher when bound to the Z-conformation (≃25 ns) than when bound to the B-conformation (≃23.7 ns). The nature of the salt has been checked. In the presence of 2.5M NaClO4, no transition from the Z-conformation to another conformation is observed when EB is added. On the contrary, in the presence of 4.25M NaCl, EB induces a cooperative transition from the Z-conformation to a conformation characterized by a much higher affinity for EB intercalation. In the case of poly(dG-dC) this last conformation is identical to the one observed at low ionic strength (B-conformation), but in the case of the platinated polymer this conformation is slightly different, as judged by the smaller value of the fluorescence lifetime of the intercalated EB.
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    Biopolymers 25 (1986), S. 539-554 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intensities of polarized fluorescence from ethidium bound to phage λ DNA undergoing agarose gel electrophoresis were measured. The intensities were strongly field dependent at voltage gradients of 8 V/cm, consistent with a partial orientation of DNA helices in the direction of electrophoresis about 500 times larger than seen in the same field in solution. Such an orientation was predicted by a reptation model of gel electrophoresis advanced by Lumpkin et al. [(1985) Biopolymers, 24, 1573-1593]. The present results can be fit successfully to this theory with a single adjustable parameter, the gel-DNA contact distance. Also, λ DNA electrophoretic mobilities in the same concentration gel were determined using the same buffer system. Both orientation and mobility measurements can be fit to the reptation theory within a factor of two using the same values of two parameters, the gel-DNA contact distance and the ratio of DNA charge to frictional coefficient.
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    Biopolymers 25 (1986), S. 527-537 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The association of heparin with thrombin was investigated by fluorometric titration. A maximum of 25% of the fluorescence of fluorescein-labeled heparin (FTC-heparin) was quenched at thrombin saturation in the absence of NaCl. FTC-heparin (H) associated tightly with thrombin (T) and the association constant of the ternary complex, H2T, formed in the absence of NaCl, was calculated to be 1.7 × 108M-1. However, the association was strongly influenced by the NaCl concentration, and the association constant of the equimolar complex, HT, formed in 0.15M NaCl was found to be 1 × 106M-1. The first-order rate constant, kapp, for inactivation of thrombin by antithrombin III (AT III) and low-affinity heparin (LA-heparin) was comparable with that of high-affinity heparin (HA-heparin) in the absence of NaCl, but decreased with an increase in the concentration of NaCl. The decreased enhancement of the thrombin-AT III reaction by LA-heparin at high NaCl concentration appeared to result from a decreased association of thrombin with LA-heparin, thus reducing the formation of the ternary complex, thrombin-LA-heparin-AT III.
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    Biopolymers 25 (1986), S. 607-625 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-diffraction pattern of an oriented film of poly(α-aminoisobutyric acid) in the 310-helical conformation has been analyzed. The conformation was obtained by a linked-atom least-squares refinement of average values from crystal structures. Specimens treated with dichloracetic acid, to improve their crystallinity, conform to space group R3c with a = 21.8 Å, c = 5.95 Å. The structure contains channels that can accommodate molecules of dichloracetic acid. One molecule of acid per six residues fills the channels, and the R-factor then is 34% using 23 reflections. Ir evidence is presented to show that the acid may hydrogen bond to the peptide groups. Some reflections occasionally observed on the diffraction photographs are attributed to a 15/4 α-helix. The significance of the results is considered in relation to Aib-containing peptides.
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    Biopolymers 25 (1986), S. 639-654 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four different types of ir experiments, involving changes in pH, changes in pressure, and the use of nonaqueous solvents, and with either albumin molecules dissolved in saline or adsorbed albumin films, support the hypothesis that the bandwidth of the amide I vibration of albumin is directly related to the amount of bound water in this protein. From the amide I band narrowing and the amide I shift to higher frequencies, it is proposed that a more ordered helix structure results as the amount of bound water is decreased.
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  • 55
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    Topics: Chemistry and Pharmacology
    Notes: We have recorded one-dimensional exchangeable proton and two-dimensional nonexchangeable proton nmr spectra on the complex of netropsin with the self-complementary d(G-G-T-A-T-A-C-C) duplex in aqueous solution between 25° and 35°C. The antibiotic amide, pyrrole, and methylene protons, and the nucleic acid base and sugar H1′, H2′, H2″, and H3′ protons, have been assigned from an analysis of the two-dimensional nuclear Overhauser effect (NOESY) spectra of the complex. We observe intermolecular NOEs between the antibiotic concave face amide, pyrrole, and CH2 resonances, and the adenosine H2 and sugar H1′ protons of base-pairs T3·A6 and A4·T5 in the central TATA core of the d(G1-G2-T3-A4-T5-A6-C7-C8) duplex. We present a molecular model outlining these seven antibiotic-DNA contacts for the complex in solution. The observed line-broadening of several base and sugar protons at the TATA minor groove netropsin binding site in the complex at 35°C are interpreted in terms of intermediate exchange between two orientations of bound netropsin on the duplex.
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  • 56
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The amino acid sequence of the collagen α1(I) chain (calf) is analyzed. Deviations of random tripeptide distribution leads to the definition of clusters. Inside these regions, collagen-typical tripeptides are located. Besides Gly-Pro-Hyp, Gly-Pro-Ala, and Gly-Ala-Hyp, the polar sequences Gly-Glu-Hyp, Gly-Ala-Arg, Gly-Glu-Arg, and Gly-Pro-Lys form typical sequences. The neighborhood of each tripeptide is analyzed and classified. The proximity to the collagen-typical tripeptides is registered. Cluster theory: Less-typical sequences also fold as members of the collagen triple helix and they are as reasonable as well as important for the collagen structure as the cluster tripeptides, but only the latter are important for the nucleation of the triple-helical folding.
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    Biopolymers 25 (1986), S. 1087-1093 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent accessible peptide bonds in proteins exhibit a 1-3° compression of the OCN bond angle and a corresponding expansion of the NCCa bond angle, relative to buried peptide bonds. These changes are consistent with an increase in hydrogen bonding to the carbonyl oxygen accompanying solvent exposure (J. D. Dunitz and F. K. Winkler, (1975) Acta Cryst. B31, 251-263). For amphiphilic structures such as α-helices, systematic differences in peptide-bond geometry between solvent-exposed and buried residues will generate significant curvature. A decrease of 4° in the OCN bond angle between hydrophilic and hydrophobic sides of an amphiphilic helix will lead to smooth bending, with a radius of curvature of about 70 Å. This curvature is in the range observed for α-helices in proteins. Helix curvature is estimated to have only a small effect on the magnitude and direction of the helical dipole moment.
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    Biopolymers 25 (1986), S. 1157-1175 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small-angle neutron scattering (SANS) was used to examine concentrated bovine serum albumin solutions of up to 20% protein w/v. At higher protein concentrations, scattering data show distinct features that can be ascribed to strong intermolecular interactions. Differential scattering cross-sections are fitted to a theoretical model of interparticle potential consisting of a hard core plus an exponentially decaying “tail.” For moderate ionic strength (0.03M K Acetate, pH 5.9), the intermolecular interaction agrees with the double-layer repulsive part of the well-known DLVO (Derjaguin, Landau, Verwey, Overbeek) theory for interacting colloidal particles. We thus demonstrate that it is possible to determine size parameters and the surface charge of protein molecules in dense solutions. At high salt concentrations (≥0.2M NaCl) data can be fitted by the same potential model, although interpretation in terms of DLVO theory is not possible. Even in this case, however, “effective” molecular size and potential parameters can be determined.
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    Biopolymers 25 (1986), S. 1179-1184 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Biopolymers 25 (1986), S. 1229-1247 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A computational method for attempting to predict protein complexes from the coordinates of the individual proteins has been developed. It is based on matching complementary patterns of knobs and holes. The computer algorithm correctly and uniquely predicts the association of the alpha and beta subunits to form the αβ dimer corresponding to the α1β1 interface in the hemoglobin tetramer. It fails to correctly dock trypsin inhibitor onto trypsin. Nevertheless, this lone success is still a significant advance over previous protein-docking algorithms. The method is also important because it introduces several ways to measure the shape of protein surface regions.
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    Biopolymers 25 (1986), S. 1209-1228 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the interactions of the substitution-inert inversion-labile complexes Fe(bipy)32+ and Fe(phen)32+ [and the inversion-stable complex Ru(bipy)32+] with DNA. The association of these complexes to DNA is mainly electrostatic, and Fe(phen)32+ shows a more effective binding to DNA than the two bipyridyl complexes, possibly owing to a different binding mode. The interactions are enantioselective, leading to a Pfeiffer shift in the diastereomeric inversion equilibria and an excess of the Δ-enantiomer of Fe(phen)32+ and Fe(bipy)32+, which is directly monitorable through CD. The partition constants for the inversion equilibrium range from 1.3 to 2.0 for Fe(bipy)32+ and Fe(phen)32+, depending on ionic conditions. From flow LD information about the orientation of the complexes on DNA was obtained: it is consistent with a fit of the Δ-enantiomer in the major groove of the right-handed DNA helix. The mechanisms of interaction are discussed against equilibrium, spectroscopic, and kinetic data.
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    Biopolymers 25 (1986), S. 1283-1297 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distribution of bound Mn2+ ions about poly(rI)·poly(rC) has been studied by measuring the effect of this paramagnetic metal ion on the relaxation behavior of poly(rI)·poly(rC) protons. By combining selective spin - lattice and spin - spin relaxation rates for various protons, some of the principle regions of ion association can be identified. The relaxation data on the CH6 proton are consistent with a 〈 10% occupancy of phosphate inner-sphere binding sites. The broadening of the imino proton resonance requires a substantial occupancy of sites located in the major groove, possibly near IN7. This would also be consistent with the observation that IH8 resonance is the proton most susceptible to relaxation by Mn2+. The relaxation data for the IH2 proton indicate a relatively low occupancy of minor-groove binding sites (e.g., IN3).
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  • 63
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The combination of ultrafiltration and difference spectroscopy allows the quantitative determination of spectra of thionine bound to heparin. The spectra of the bound dye do not depend on the degree of coverage; this and the shape of the Scatchard plot show that “all-or-none” binding is valid. A calculus of variations based on a modification of the Hill plot shows that aggregates of seven thionine cations are bound. Tetrasaccharides with an average charge of two carboxylate and five sulfate groups are suggested to be the binding sites. The binding constant given for one mole thionine is 4.4 · 105 M-1. The Gibbs enthalpy for binding of one mole of thionine is -31.7 kJ·M-1 at 20°C.
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  • 64
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of ethidium's intercalative binding to DNA packaged in bacteriophage T7 and two T7 deletion mutants have been determined, using enhancement of fluorescence to quantitate binding. At a constant ethidium concentration, the results can be described as first-order binding with two different rate constants, k1* (= k1 + k-1) and k2* (= k2 + k-2). The larger rate constant (k1*) was at least four orders of magnitude smaller than the comparable first-order forward rate constant for binding to DNA released from its capsid. At 25°C values of k1* decreased as the amount of DNA packaged per internal volume increased. This latter observation indicates that the rate of ethidium's binding to packaged T7 DNA is limited by an event that occurs inside of the DNA-containing region of T7, not by the crossing of T7 capsid's outer shell. Arrhenius plots of kM1* are biphasic, indicating a transition for packaged DNA at a temperature of 20°C. The data indicate that k1* s are limited by either sieving of ethidium during its passage through the packaged DNA or subsequent hindered intercalation.
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  • 65
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    Biopolymers 25 (1986) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 66
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    Biopolymers 25 (1986), S. 1399-1417 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The three-dimensional structure was determined by x-ray crystallography for d(T[p](CE)T), a uv photoproduct of the cyanoethyl (CE) derivative of d(TpT), having the cis-syn cyclobutane (CB) geometry and the S-configuration at the chiral phosphorus atom. The crystals of C23H30N5O12P · 2H2O belong to the orthorhombic space group P212121 (Z = 4), with cell dimensions a = 11.596 Å, b = 14.834 Å, and c = 15.946 Å, containing two water molecules per asymmetric unit. The CB ring is puckered with a dihedral angle of 151°. The two pyrimidine bases are rotated by -29° from the position of direct overlap of their corresponding atoms. This represents a major distortion of DNA, since in DNA adjacent thymines are rotated by +36°. The pyrimidine rings are puckered with Cremer-Pople parameters for T[p] and in parentheses [p]T: Q: 0.24 Å (0.31 Å); θ: 123° (120°); φ: 141° (86°). These represent half-chairs designated as 6H1 (T[p]) and 6H5 ([p]T). The CB and pyrimidine ring conformations are interrelated, and we postulate that they execute a coupled interconversion in solution. The T[p] segment has the syn glycosyl conformation, a 2T3 sugar pucker, and gauche- conformation at C4′-C5′; the [p]T segment is anti, 3T4, trans. The C5′-O5′ torsion of the [p]T unit is -124.5°, and the C3′-O3′ torsion of the T[p] unit is -152.9°. Bond angles and bond lengths involving the phosphorus atom are similar to those of other phosphotriesters. The P-O3′ and P-05′ torsion angles are -138.1° and 58.6°, respectively. Several intermolecular (but no intramolecular) hydrogen bonds are found in the crystal.
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    Biopolymers 25 (1986), S. 1505-1517 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Light-scattering techniques have been used to measure the z-average radius of gyration Rg z-average translational diffusion coefficient Dt and weight-average molecular weight Mw of porcine submaxillary mucin (PSM) in solution. PSM isolated at low shear in the presence of protease inhibitors has a Mw about twice as large as a sample prepared without these precautions. The former sample has a Mw of 17 × 106 in 0.1M NaCl, which decreases to 8 × 106 in 6M guanidine hydrochloride (GdnHCl) and then to 2 × 106 on addition of 0.1M mercaptoethanol to the 6M GdnHCl solution. The Rg or D-1t values obtained for PSM in this work superimpose with those of other authors for different mucin glycoproteins, leading to linear log-log relationships to the molecular weight of the protein core. Comparison of these results with those in the literature for denatured proteins suggest that mucins are linear random coils in which the protein core is stiffened by the presence of the oligosaccharide side chains. The length of the oligosaccharides and the nature of the solvent have little effect on the extension of the protein core. This suggests that the stiffness of the protein core is maintained by steric repulsion of the residues at the beginning of the oligosaccharide chains.
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    Biopolymers 25 (1986), S. 1493-1504 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of melittin, a surface-active polypeptide, in solution was studied by CD spectra between 190 and 240 nm. The molecule was essentially unordered (possibly with a trace of helix) in water without salt at neutral pH. Upon deprotonation of four of the six cationic groups at pH 12 the polypeptide became partially helical (about 35%). The addition of NaDodSO4 to an aqueous melittin solution first caused the solution to become turbid but it became clear again in excess surfactant solution. The conformational changes depended on the molar NaDodSO4/melittin ratio, R. With R from 2.34 to 23.4, the melittin solution was turbid and the polypeptide conformation was probably a mixture of α-helix and β-sheets. This was supported by the ir spectrum of the turbid solution, which indicated the presence of both conformations. With R = 46.8 or 468 (1 or 10 mM NaDodSO4) the polypeptide conformation was characteristic of an α-helix, about 70-80% of the molecule, regardless of whether the surfactant was above or below its critical micelle concentration. This compared well with the x-ray results of 92% helix in crystals. The lower helicity of melittin in NaDodSO4 solution might be attributed to the end effects that destabilize the first and last turn of an helix at its N- and C-terminus, respectively.
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    Biopolymers 25 (1986), S. 1565-1577 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Short segments of polypeptide, from a protein for which the primary sequence but not the three-dimensional structure is known, are compared to a library of known structures. The basis of comparison is the probability with which residues in the unknown segment might substitute through evolution for residues in segments of known structure. In test cases, segments from known structures that are similar in sequence to those from a protein treated as unknown are often found to be similar in three-dimensional structure to one another and to the true structure of the “unknown” segment. This provides a basis for prediction of the local configuration (secondary structure) of polypeptides.
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    Biopolymers 25 (1986), S. 1603-1606 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Biopolymers 25 (1986), S. 1615-1621 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: X-ray diffraction studies have been carried out on a single crystal of the photosynthetic inhibitors N-(3,4-dichlorophenyl)-N′-dimethylurea (DCMU) and its newly synthesized spin-labeled analog N-(3,4-dichlorophenyl)-N′-(3,3,5,5-tetramethylpiperidine-4-oxyl)-urea (DTPU). The synthesis of DTPU as well as its crystallographic data are reported. The crystal system of both compounds is monoclinic with a space group P21/c. The cell constants of DCMU are a = 7.759(1), b = 14.737(3), c = 9.233(2) Å, β = 100.99(6)°; of DTPU they are a = 6.976(1), b = 11.998(2), c = 23.585(3) Å, β = 91.38(5)°. Comparison of conformational parameters of DCMU and DTPU reveal differences in the dihedral angle between the aromatic ring and the ureido plane. The measured volumes of DCMU and DTPU are 259.1 and 493.3 Å3, respectively. These figures suggest the size of the binding site of the inhibitors in the photosynthetic membrane.
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  • 72
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational analysis of a protected homodipeptide of 1-aminocyclopentanecarboxylic acid (Acc5) has been carried out. 1H-nmr studies establish a β-turn conformation for Boc-Acc5-Acc5-NHMe in chloroform and dimethylsulfoxide solutions involving the methylamide NH in an intramolecular hydrogen bond. Supportive evidence for the formation of an intramolecular hydrogen bond is obtained from ir studies. X-ray diffraction studies reveal a type III β-turn conformation in the solid state stabilized by a 4 → 1 hydrogen bond between the Boc CO and methylamide NH groups. The φ,ψ values for both Acc5 residues are close to those expected for an ideal 310-helical conformation (φ≃ ± 60°, ψ∼ ±30°).
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    Biopolymers 25 (1986), S. 1685-1695 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decrease in mobility of viscous glycol-water solvents when associated with native DNA is quantified from a study of the loss of the exciting-wavelength dependence of the phosphorescence spectrum of free and bound proflavin with increasing temperature. The data are interpreted in terms of a distribution of rate constants with an Arrhenius temperature dependence. Over the temperature range of the experiments a relative decrease of ∼ 104 in the average rate constant is observed for reorientation of the solvent when associated with DNA. The basis for this large reduction is found to derive from a large decrease in the pre-exponential factors (i.e., activation entropy) associated with the reorientation rate constants. The changes in the distribution of rate constants and the activation parameters for solvent mobility induced by DNA do not resemble the changes observed for any one of a number of small ion or molecule perturbations. The results suggest the presence of disorganized, relatively immobile solvent in association with DNA.
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  • 74
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The three-dimensional Poisson-Boltzmann equation for the distribution of counterion charge density around double-helical DNA has been solved for solutions of .01M, .10M, and .20M monovalent salt. The polymers, poly[d(CpGp)] and poly[d(m5CpGp)], were studied in the B- and the Z-conformations. The effect of methylation on the relative stabilities of these conformers in solutions of different ionic strengths is known to favor the Z-form. Accumulation of charge density around the B- and the Z-conformers is compared in detail. The relative electrostatic stabilities of the B- and Z-conformers in .01M, .10M, and .20M solutions are compared and discussed in terms of the ion-DNA interactions and the self-energy of the structured ionic environment. The ion-DNA interaction energies, termed “phosphate screening,” monotonically decrease with ionic strength and are consistent with a B-to-Z conformation change induced in either polymer by increased electrolyte concentration. However, these calculated energies alone do not account for the fact that the ionic strength at the midpoint of the transition of the methylated polymer is substantially lower than that of its unmethylated analogues. The phosphate screening effect is counterbalanced by changes in the self-energy required for the creation of the structured counterion environment. This self-energy of the electrolyte environment monotonically increases with ionic strength. Methylation-induced shifts in the overall conformational equilibria depend on the relative changes of these competing effects. Increasing salt concentration is calcualted to favor the Z-conformer. The effect of methylation, lowering the ionic strength of the transition midpoint, is proposed to originate in minor structural changes in the Z-form of the polymer, making the groove more accessible to counterions in the G(3′ - 5′)C region. This allows a redistribution of counterion density and a lowering of the self-energy of the ionic environment, conferring added stability to the Z-conformation, as indicated by calculations of relative entropies. The experimentally observed temperature dependence of the B-to-Z transition, however, cannot be explained without assuming the release of bound water. Maps of the calculated three-dimensional structure at the counterion distribution near the surface of these molecules in both the B- and the Z-forms are also presented.
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  • 75
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourier transform ir vibrational circular dichroism (VCD) spectra in the amide I′ region of poly(L-lysine) in D2O solutions have confirmed the existence of three distinct conformational states and an unordered conformational state in this homopolypeptide. Characteristic VCD spectra are presented for the right-handed α-helix, the antiparallel β-sheet, an extended helix conformation previously referred to as the so-called “random coil,” and a completely unordered conformation characterized by the absence of any amide I′ VCD. VCD for the antiparallel β-sheet in solution and the unordered chain conformation are presented for the first time. Each of the four different VCD spectra is unique in appearance and lends weight to the view that VCD has the potential to become a sensitive new probe of the secondary structure of proteins in solution.
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  • 76
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hinge-bending mode of hen egg white lysozyme is studied by a constrained minimization technique. Results with and without a bound inhibitor, tri-N-acetyl-glucosamine, are obtained. The frequency of the mode with the inhibitor is found to be 4.3 cm-1, in contrast to 3.0 cm-1 for the free enzyme. Also, the hinge-bending angle with the lowest energy is shifted 10° towards a more closed cleft in the bound species. The main contribution to these differences arise from interactions with the residues lining the cleft and those on the back side of it. Structural details that account for the energetics are presented. The method of calculation is somewhat different from a previous study [J. A. McCammon, B. R. Gelin, M. Karplus & P. G. Wolynes, (1976) Nature 262, 325-326] to reduce the likelihood of artifacts in the results.
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    Biopolymers 25 (1986), S. 1859-1864 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The overall dynamics of the Pf1 filamentous bacteriophage particle in solution are characterized by nmr experiments. The chemical-shift anisotropy powder-pattern lineshapes from both DNA and protein backbone sites of the virus are motionally averaged in the same way, indicating that the entire particle undergoes rapid (〈 104 Hz) reorientation about the long axis of the filament when the virus is in solution at high pH. In contrast, the virus particles in samples at low pH are immobile on this time scale.
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  • 78
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and internal motions of the protein hen egg white lysozyme are studied by analysis of simulation and experimental data. A molecular dynamics simulation and an energy minimization of the protein in vacuum have been made and the results compared with high-resolution structures and temperature factors of hen egg white lysozyme in two different crystal forms and of the homologous protein human lysozyme. The structures obtained from molecular dynamics and energy minimization have root-mean-square deviations for backbone atoms of 2.3 Å and 1.1-1.3 Å, respectively, relative to the crystal structures; the different crystal structures have root-mean-square deviations of 0.73-0.81 Å for the backbone atoms. In comparing the backbone dihedral angles, the difference between the dynamics and the crystal structure on which it is based is the same as that between any two crystal structures. The internal fluctuations of atomic positions calculated from the molecular dynamics trajectory agree well with the temperature factors from the three structures. Simulation and crystal results both show that there are large motions for residues involved in exposed turns of the backbone chain, relatively smaller motions for residues involved in the middle of helices or β-sheet structures, and relatively small motions of residues near disulfide bridges. Also, both the simulation and crystal data show that side-chain atoms have larger fluctuations than main-chain atoms. Moreover, the regions that have large deviations among the x-ray crystal structures, which indicates flexibility, are found to have large fluctuations in the simulation.
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  • 79
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of the carbocyanine dye Stains-all with the Ca2+-binding proteins calmodulin, troponin C, and parvalbumin has been monitored by means of absorption spectra and CD. In the absence of Ca2+, complexes with Stains-all of all three proteins exhibit at high dye: protein mole ratios an intense J absorption band at 600-650 nm, which is associated with a characteristic CD spectrum. In the cases of calmodulin and troponin C, the J-band is progressively lost as the dye: protein ratio decreases and is replaced by bands of the γ and β types at 450-550 nm, which likewise give rise to characteristic CD spectra. For parvalbumin, only the J-band is observed; its intensity is undiminished at the lowest dye: protein ratios examined. In the presence of excess Ca2+ the J-band is lost for all three proteins. For calmodulin and troponin C it is replaced by σ- and β-bands; in the case of parvalbumin the bound dye is released. A tentative model has been proposed to account for these observations.
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  • 80
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The average conformation of Met-enkephalin was determined by using an adaptive, importance-sampling Monte Carlo algorithm (SMAPPS - Statistical Mechanical Algorithm for Predicting Protein Structure). In the calculation, only the backbone dihedral angles (φ and ψ) were allowed to vary; i.e., all side-chain (χ) and peptide-bond (ω) dihedral angles were kept fixed at the values corresponding to a low-energy structure of the pentapeptide. The total conformational energy for each randomly generated structure of the polypeptide was obtained by summing over the interaction energies of all pairs of nonbonded atoms of the whole molecule. The interaction energies were computed by the program ECEPP/2 (Empirical Conformational Energy Program for Peptides). Solvent effects were not included in the computation. The calculation was repeated until a total of 10 independent average conformations were established. The regions of conformational space occupied by the average structures were compared with the regions of low conditional free energy obtained by SMAPPS in the first paper of this series. Such a comparison provides an analysis of the capacity of SMAPPS to adjust the Monte Carlo search to regions of highest probability. The results demonstrate that the ability of SMAPPS to focus the Monte Carlo search is excellent. Finally, the 10 independent average conformations and the mean of the 10 average structures were utilized as the initial conformations for a direct energy minimization of the pentapeptide. Of the 11 final energy-minimized structures, three of the conformations were found to be equivalent to the conformation of lowest energy determined previously. In addition, all but two of the remaining energy-minimized structures were found to correspond to one of the two other conformations of high probability obtained in the first paper of this series. These results indicate that a set of independent average conformations can provide a rational, unbiased choice for the initial conformation, to be used in a direct energy minimization of a polypeptide. The final energy-minimized structures consequently constitute a set of low-energy conformations, which include the global energy minimum.
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    Biopolymers 25 (1986), S. 1623-1633 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interpretation of ΔGDH2O (the free energy change for the reaction, globular conformation ⇋ randomly coiled conformation, in the absence of denaturant), in terms of the free energies of transfer of various parts of the protein molecule from water to denaturant solution, is unsatisfactory because the latter are assumed to be identical to the transfer-free energies of similar groups attached to smaller model compounds. We have made empirical adjustments to transfer-free energy theory that make possible linear extrapolation of the free energy of denaturation of a protein from transition region to zero denaturant concentration. The modified theory, used to analyze the denaturation of proteins by guanidine hydrochloride and urea, allowed us to calculate reasonable values for Δα, the average change in accessibility to solvent of the component groups of protein.
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    Biopolymers 25 (1986), S. 1659-1672 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The multidimensional statistical technique of discriminant analysis is used to allocate amino acid sequences to one of four secondary structural classes: high α content, high β content, mixed α and β, low content of ordered structure. Discrimination is based on four attributes: estimates of percentages of α and β structures, and regular variations in the hydrophobic values of residues along the sequence, occurring with periods of 2 and 3.6 residues. The reliability of the method, estimated by classifying 138 sequences from the Brookhaven Protein Data Bank, is 80%, with no misallocations between α-rich and β-rich classes. The reliability can be increased to 84% by making no allocation for proteins classified with odds close to 1. Classification using previously developed secondary structural prediction methods is considerably less reliable, the best result being 64% obtained using predictions based on the Delphi method.
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    Biopolymers 25 (1986), S. 1717-1733 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distributions of charged groups in 32 proteins of known three-dimensional structure have been analyzed to determine how regularly the groups are spread over the molecule's surfaces, and to identify and to study those proteins where charge asymmetry would seem important for their function. The distributions have been analyzed in terms of charge “polarity,” surface “charge density,” and electric dipole moments. More detailed studies of the distributions for individual proteins are made using map projections specifically developed for this purpose. In the light of the results obtained we discuss the role of charged groups in relation to protein function.
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    Biopolymers 25 (1986) 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Biopolymers 25 (1986), S. 1803-1812 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Changes in the 31P-nmr spectra of sonicated natural DNA fragments were investigated in ethanol solutions where the fragments underwent, as checked by CD, the B-to-A conformational transition. The study produced the following conclusions: (1) The high DNA concentrations used for the 31P-nmr measurements promote the transition compared to dilute solutions that are commonly used for CD measurements. (2) The B-to-A transition was reflected in a cooperative downfield shift of the DNA 31P-nmr resonance, consistent with unwinding of the double helix. (3) Prior to the transition, the changes in chemical shift of double-and single-stranded DNAs were almost identical. It thus appears that the effect of ethanol on the geometry and hydration of phosphodiester linkages does not depend heavily on DNA base-base interactions. (4) The A-form resonances were 30-40% narrower than the B-form resonances, which is attributed to marked sequence-dependent variations in the latter conformation and to their reduction in the former. (5) The B-form DNA aggregated in the concentrated 31P-nmr samples in the presence of ethanol, judged from a milky opalescence of the solution and a substantial broadening of its 31P-nmr resonance. The broadening abruptly disappeared as soon as DNA adopted the A-form so that DNA, in dependence on the secondary structure, showed different tendencies to condense in the presence of ethanol. The condensation increased cooperativity of the B-to-A interconversion.
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  • 86
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monte Carlo computer simulations were performed to elucidate the dynamic aspects of the folding and unfolding transitions of island-model protein. Five different types of model proteins were designed, according to characteristics of backbone structure. The computer simulations clearly show that the unfolding and folding transitions are all-or-none processes between the N-and U-states. They are typical Poisson processes. From the Arrhenius plots of rate constants, the activation enthalpies of folding and unfolding were determined. In addition, the folding pathways were determined along the reaction coordinate. Formations of several local structures along a polypeptide chain are almost simultaneous, but the most probable time sequence of events exists at the moment of transition. That is the most probable folding pathway. The unfolding pathway was found to be just the reverse process of the most probable folding pathway. The relationship between the fluctuations in each equilibrium state and the transition process was considered. In contrast to the theory of absolute reaction rate, the transient states are widely distributed along the reaction coordinate. From analysis of the “transient process,” we tried to determine the critical states from which the transient process starts. As a result, we found that the unfolding transition occurs at the stage near the N-state. During the U-state, large joined blocks rarely appear, but they appear in the transient process towards the N-state. However, the “branch point” between the N- and U-states lies near the N-state, and joined blocks tend to unfold prior to passing over the branch point. We concluded that the stability of later folding intermediates is important for selection of the folding pathway, while preferential selection of an early folding intermediate is important in acceleration of the folding rate. The effects of intrachain cross-linking and peptide fragment binding on the rate constants were examined by using computer simulations of model proteins. In general, a small-sized loop formed by cross-linking accelerates the folding rate and a large-sized loop contributes much to the stabilization of the native conformation. We also found that peptide fragment binding contributes little to the acceleration of the folding rate of the residual protein.
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  • 87
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    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1875-1893 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heat denaturation of pepsinized bovine nonfibrillar and fibrillar collagen was studied by differential scanning calorimetry. For fibrillar preparations that had been rapidly precipitated with stirring at low ionic strength, then resuspended at physiological ionic strength, multiple denaturational transitions were observed. At heating rates of 10°C/min, melting endotherms occurred at about 44, 50, 53, and 57°C. Fibrillar collagen that was slowly gelled without stirring at physiological ionic strength exhibited a similar series of endotherms, but the lower melting transitions were less conspicuous. In contrast, nonfibrillar bovine collagen in acidic solution showed only a single denaturational transition at 40°C. Nonfibrillar solutions at pH 7, to which inhibitors of fibrillogenesis were added, showed a major endotherm as high as 46°C. These results suggest that reconstituted fibrillar collagen contains a heterogeneous fibril population, possibly including molecules in a nonfibrillar state. It was proposed that the multiple melting endotherms of such preparations were due to sequential melting of molecular and fibril classes, each with a distinct melting temperature. The fibrillar classes may represent three or more types of banded and nonbanded species that differ from each other in packing order, collagen concentration, and possibly also in fibril width and level of cross-linking.
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  • 88
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton nmr and CD spectra of gramicidin S (GS) cyclic-(Val1,1′-Orn2,2′-Leu3,3′-D-Phe4,4′-Pro5,5′)2 and of GS analogs - namely, [D-Ala4,4′]-GS, [Gly4,4′]-GS, and [L-Ala4,4′]-GS - were analyzed. The molecular conformation of [D-Ala4,4′]-GS is similar to that of GS, with the trans form about the D-Ala-Pro peptide bond. The molecular conformation of [Gly4,4′]-GS depends on the solvent composition of dimethylsulfoxide-d6/trifluoroethanol (DMSO)-d6/TFE and DMSO-d6/H2O as well as the solute concentration. In DMSO-d6 solution, [Gly4,4′]-GS forms the GS-type conformation of the monomer at lower concentration. At higher concentration, the GS-type conformer is converted to the other one that forms molecular aggregates. The cis form about the X-Pro peptide bonds is found for [Gly4,4′]-GS and [L-Ala4,4′]-GS in DMSO-d6 and for [L-Ala4,4′]-GS in TFE solution. The large temperature dependences of α-proton chemical shifts of [L-Ala4,4′]-GS in DMSO-d6 solution indicate that the conformer equilibrium changes with temperature. The GS-type conformation is not formed in [L-Ala4,4′]-GS. The two active peptide analogs, [D-Ala4,4′]-GS and [Gly4,4′]-GS, interact with the phospholipid membrane, taking the GS-type conformation. By contrast, an inactive analog, [L-Ala4,4′]-GS, does not interact with phospholipid membrane. The activities of GS analogs are found to correlate to the formation of the GS-type conformation upon binding with phospholipid membrane.
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  • 89
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    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2359-2373 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distinctive transverse banding pattern of fibrin fibers clearly indicates ordering of molecules in the longitudinal direction. In this study we examined the fibers of fibrin clots, as well as two types of fibrinogen polymers, by thin-section electron microscopy. The fibrinogen polymers have a transverse banding pattern identical to that of fibrin fibers - clearly indicating a regular longitudinal repeat - but they are larger in diameter, and show little or no branching. We therefore expected their overall ordering to be better than that of fibrin fibers. Several different fixation protocols were used. We readily observed the typical transverse banding seen previously by negative stain and metal replication techniques. However, only very rarely was any regular lateral lattice seen in any of the samples. X-ray diffraction was used to examine unfixed specimens of the two fibrinogen polymers and, once again, although a longitudinal repeat was evident, only rarely was evidence for lateral crystallinity seen. The electron-microscope and x-ray results showed that the needles and pellet fibers of fibrinogen have essentially the same internal architecture as thick fibrin fibers, and that all three types of polymer, although clearly transversely banded, have almost no crystallinity in their lateral protofibril packing.
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  • 90
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the formation of the complex between bovine β-trypsin and the porcine pancreatic secretory trypsin inhibitor (PSTI; Kazal-type inhibitor) was investigated following the spectral changes associated with the displacement of proflavine from the enzyme, upon inhibitor binding, between pH 3.5 and 8.0 (I = 0.1M) at 21 ± 0.5°C. With inhibitor in excess over the enzyme ([PSTI] ≥ 5 × [bovine β-trypsin]), the time course of the reaction corresponds to a pseudo-first-order process. Over the whole pH range explored, the concentration dependence of the rate is second order at low PSTI concentrations but tends to first order at high inhibitor concentrations. This behavior may be explained by a relatively fast pre-equilibrium followed by a limiting first-order process. Values of kinetic parameters for PSTI binding to bovine β-trypsin depend, between pH 3.5 and 8.0, on the acid-base equilibrium of a single ionizing group (probably His-57 of bovine β-trypsin) that undergoes an acidic pKa shift from 7.0 in the free bovine β-trypsin to 5.5 in the enzyme:PSTI complex. Kinetics of the bovine β-trypsin:PSTI adduct formation has been analyzed and compared with that of other (pro)enzyme:inhibitor reactions. Considering the known molecular structures of free serine (pro)enzymes, of Kazal- and Kunitz-type inhibitors, as well as of their complexes, the binding behavior of PSTI to bovine β-trypsin has been related to the inferred stereochemistry of the proteinase:inhibitor contact region.
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  • 91
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 67-67 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 92
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 67-67 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 93
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 77-84 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 94
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983) 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 95
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 202-202 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 96
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 97
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 20 (1986), S. 1-10 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 14 Ill.
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  • 98
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. xi 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 99
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 33-36 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potential-energy calculations are reported on the interaction between two collagenlike triple-stranded poly(Gly-L-Pro-L-Pro) helices. Short helices can pack in a variety of orientations, but there is a unique parallel packing arrangement of the two helices for longer polypeptide chains.
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  • 100
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    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 43-47 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The lattice model of Flory has been extended in order to consider equilibrium between isotropic and nematic phases containing helix-coil type chains. Nearly complete exclusion of coil sequences from the lyotropic nematic phase produces an enhanced cooperativity in the helix-coil transition. In poor solvents this enhancement begins to occur at concentrations typical of some experiments.
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