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  • Digitale Medien  (7)
  • Chemistry  (7)
  • 1
    Digitale Medien
    Digitale Medien
    Solution behavior of α-chymotrypsin dissolved in nonpolar organic solvents via hydrophobic ion pairing (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 451-456 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dissolution of α-chymotrypsin in nonpolar organic solvents can be achieved using hydrophobic ion pairing, whereby the polar counterions are replaced by a stoichiometric number of detergent molecules. Using Aerosol OT[AOT, sodium bis(2-octyl)sulfosuccinate], it is possible to partition significant amounts of the enzyme into alkanes and chlorocarbons. Apparent solubility in isooctane is greater than 1 mg/mL (80 μM). Necessary conditions for achieving effective partitioning of α-chymotrypsin into these solvents are described. Using CD spectroscopy, it can be shown that the AOT-α-chymotrypsin (CMT) complex retains its native secondary and tertiary structure when dissolved in alkanes, and that the globular structure is stable to more than 100°C. In contrast, α-chymotrypsin unfolds at 54°C in aqueous solution. The relative solubility of the AOT-CMT complex in a variety of alkanes and chlorocarbons is also reported. The native structure of α-chymotrypsin is maintained in carbon tetrachloride, but not in methylene chloride or chloroform. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360350504
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  • 2
    Digitale Medien
    Digitale Medien
    Molecular orbital calculations on the oligopeptides netropsin, distamycin and related compounds (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2065-2082 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electronic structure of the antibiotics netropsin, distamycin A, and related compounds has been examined by various theoretical models. Calculations of both the Pariser-Parr-Pople (PPP) and the semiempirical CNDO/S types can account for the absorption spectrum of netropsin and distamycin A. The CD spectrum has been calculated for the conformation of netropsin found in the crystal structure of a netropsin/DNA dodecamer. Not all the CD spectral features can be attributed entirely to the chiral conformation of netropsin, indicating that there are significant interactions between netropsin and DNA. A CD calculation was also performed for distamycin A in a similar conformation. An examination of the charge-density maps of the excited states suggests that there is substantial charge transfer from the pyrrole ring to either of the adjacent peptide linkages in these systems. At higher energies, even longer distance charge transfer can be observed. Similar behavior was seen in the monomers pyrrole-2-carboxamide and 3-(formylamino)pyrrole.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360251104
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  • 3
    Digitale Medien
    Digitale Medien
    Theoretical CD studies of polypeptide helices: Examination of important electronic and geometric factors (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 569-586 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N-methylacetamide. Four discrete peptide-localized transitions were employed: π0π*(NV1), π+π* (NV2), nπ*, and n′π*. Inclusion of the π+π*transition (λ0 = 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180-250-nm region. Spectra were computed for various helical structures, including right-handed α-, αII-, ω-, π-, 310-, and poly(proline)I-helices, and the left-handed poly(proline)II-helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground-state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calculations on the α-helix has been diminished.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360310511
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  • 4
    Digitale Medien
    Digitale Medien
    The helix-coil transition in heterogeneous peptides with specific side-chain interactions: Theory and comparison with CD spectral data (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1605-1614 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Natural and synthetic peptides that contain detectable intramolecular α-helical structure in aqueous solution have been used to evaluate the helical propensities for the common amino acids. Experimental spectroscopic data must be fit to a model of the helix-coil transition in order to determine quantitative stability constants for each amino acid. We present here a statistical mechanical description of helix formation in peptides or protein fragments that takes into account multiple internal conformations, heterogeneity in the stabilizing effects of different side chains, and specific side-chain-side-chain interactions. The model enables one to calculate values of [θ]222 for a given peptide using the length dependence of the helix signal computed by a quantum mechanical treatment of the nπ* transition that dominates the 222-nm band. In addition, the helical probability at any residue in the chain is readily computed, and should prove useful as nmr spectral data become available. The free energy of specific side-chain interactions, including ion pair formation, can be evaluated. Application of the analysis to experimental data on a pair of isomeric peptides, only one of which contains ion pairs, indicates that forming a single glutamate-lysine ion pair stabilizes the α-helix by 0.50 kcal/mole in 10 mM sodium ion and pH 7. A survey of the CD data measured for a variety of model peptides is presented, indicating that a single set of s values and σ constant can account for some but not all of the available results.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360311315
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  • 5
    Digitale Medien
    Digitale Medien
    Theoretical determination of the CD of proteins containing closely packed antiparallel β-sheets (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1731-1752 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Proteins containing two closely packed β-sheets comprise an important class of biopolymers. Rotational and dipole strengths have been determined by the excition coupling model for interacting pairs of two idealized flat β-sheets and for the double β-sheets of seven globular proteins: plastocyanin, human prealbumin, immunoglobulin VREI, concanavalin A, Cu,Zn superoxide dismutase, staphylococcal nuclease, and elastase. The effects of various geometrical factors on the CD spectra were investigated. Results for the idealized sheets indicate that two sheets display through-space interactions that are large at distances of 5-7 Å and remain significant even at distances typical of the intersheet separations in globular proteins (12-15 Å). The CD spectra are sensitive to the angle (Ω) between the strand directions of the two sheets, with maximum intersheet contributions at Ω = ±45°. Both the intrastrand and interstrand twisting were determined in the seven proteins, and their effects on the calculated CD are discussed. This work represents the first theoretical CD study on the interactions of two regular protein secondary structures, including rotational strength calculations on large sections (up to 135 residues) of globular proteins.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360261007
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  • 6
    Digitale Medien
    Digitale Medien
    Enhanced solubility of proteins and peptides in nonpolar solvents through hydrophobic ion pairing (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 927-932 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new technique for enhancing the solubility of peptides and proteins in organic solvents is described. Complexation of polypeptides with stoichiometric amounts of an anionic detergent, such as sodium dodecyl sulfate (SDS), produces diminished aqueous solubility, but enhanced solubility in organic solvents. Consequently, the partitioning of a polypeptide into a nonpolar solvent can be increased by two to four orders of magnitude. In the case of an insulin-SDS complex, the solubility in 1-octanol is more than tenfold greater than in water. In 1-octanol, the native structure of insulin remains intact, as determined by CD spectroscopy, and the thermal denaturation temperature (Tm) is increased by approximately 50°C relative to unfolding in water. Finally, peptides and proteins can be extracted back into an aqueous phase provided the chloride concentration is sufficient to displace bound detergent molecules. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360330608
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  • 7
    Digitale Medien
    Digitale Medien
    Approaches for increasing the solution stability of proteins (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 48 (1995), S. 506-512 
    Details
    ISSN: 0006-3592
    Schlagwort(e): protein stabilization ; urokinase ; denaturation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Stabilization of proteins through proper formulation is an important challenge for the pharmaceutical industry. Two approaches for stabilization of proteins in solution are discussed. First, work describing the effect of additives on the thermally induced denaturation and aggregation of low molecular weight urokinase is presented. The effects of these additives can be explained by preferential exclusion of the solute from the protein, leading to increased thermal stability with respect to denaturation. Diminished denaturation leads to reduced levels of aggregation. The second approach involves stoichiometric replacement of polar counter ions (e.g., chloride, acetate, etc.) with anionic detergents, in a process termed hydrophobic ion pairing (HIP). The HIP complexes of proteins have increased solubility in organic solvents. In these organic solvents, where the water content is limited, the thermal denautration temperatures greatly exceed those observed in aqueous solution. In addition, it is possible to use HIP to selectively precipitate basic proteins from formulations that contain large amounts of stabilizers, such as human serum albumin (HSA), with a selectivity greater than 2000-fold. This has been demonstrated for various mixtures of HSA and interleukin-4. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260480513
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