ISSN:0006-3525    

DOI:10.1002/bip.360250102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have measured the VCD of polytyrosine in the amide I and II regions in dimethyl sulfoxide (DMSO) and in 80:20 mixtures of DMSO with trifluoroethanol, trifluoroacetic acid (TFA), and dichloroacetic acid and in 50:50 mixtures of DMSO and trimethyl phosphate (TMP). Additionally, VCD was obtained for deuterated polytyrosine in DMSO and DMSO:D2O, DMSO:TFA(d1), and DMSO:TMP mixtures as before. Amide A VCD was obtained in DMSO and DMSO:TMP mixtures. In the pure solvent, VCD of an opposite sign was seen as compared with that seen in the mixtures. The latter were characteristic in sign pattern and shape of right‐handed α‐helices for poly(L‐tyrosine). The pure polytyrosine:DMSO results are similar to those of polylysine:D2O at neutral pH and poly(β‐benzyl‐aspartate) in DMSO and may be characteristic of rand

ISSN:0006-3525    

DOI:10.1002/bip.360250103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractMononucleotide 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

ISSN:0006-3525    

DOI:10.1002/bip.360250104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractIn order to optimize the use of proteins as functional ingredients in foods, one needs more insight into the effects of environmental conditions (pH, ionic strength, and temperature) on the functional properties of protein. This paper summarizes the results of an extensive study on heat‐induced gelation of ovalbumin (egg‐white protein) and soybean protein in the concentration range from 10 to 35 g/100 g. It was the aim of the study to relate the rheological properties of thermally induced protein gels to the microstructure of the gel and the physicochemical properties of the constituent protein. The gelling behavior of the protein was quantified with rheological techniques, and the physical properties of the gels were determined, at small and large deformations. From the swelling/dissolving behavior of the gels in various media, the nature of the crosslinks was determined qualitatively. The microstructure of the gels was determined with electron microscopy. Nmr‐spectroscopy was applied in order to elucidate changes in conformation during heating. It was found that the formation of a continuous covalently crosslinked network is not a prerequisite for thermally‐induced protein gelation. The properties of a gel strongly depend on the pH at which the gel is formed. When heat‐set at high pH(pH∼10), a homogeneous, strong, and almost transparent gel is formed, consisting of flexible crosslinked protein gels. Heat‐setting at low pH (pH 5) leads to the formation of a heterogeneous and weak gel, which easily exudes water. This gel consists of crosslinked aggregated protein. The ionic strength of the solvent in which the protein is dissolved and heat‐set has a much lower effect on

ISSN:0006-3525    

DOI:10.1002/bip.360250105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe conformational transitions of synthetic basic polytripeptides (Lys‐Leu‐Gly)n, (A2bu‐Leu‐Gly)n, (Lys‐Leu‐Ala)n, and (A2bu‐Leu‐Ala)ninduced by high salt concentrations and elevated pH were investigated by CD, ir, and1H‐nmr spectroscopy, sedimentation analysis, viscometry, and light scattering. Sheet aggregates of chains in a conformation similar to the polyglycine II (polyproline II) helix, bound together by hydrogen bonds, are the most probable form of (Lys‐Leu‐Gly)nand also, partly, of (A2bu‐Leu‐Gly)nin a high‐pH or high‐salt solutions. The conformation (Lys‐Leu‐Ala)n, in a low‐salt concentration, is an α‐helix. Since (A2bu‐Leu‐Ala)nis disordered under similar conditions, it appears that this α‐helix is stabilized by hydrophobic interactions between Lys and Leu side chains. In a high concentration of water structure‐making ions, CD data for (Lys‐Leu‐Ala)nindicate distortion of the α‐helix, with a parallel increase in the average molecular weight corresponding to trimer formation. Hydrodynamic data are consistent with a model of bundles of three closely touching spherocylinders. (A2bu

ISSN:0006-3525    

DOI:10.1002/bip.360250106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have measured vibrational CD spectra in the 3600–1250 cm−1region of two monodisperse, protected octapeptides, which form right‐handed 310‐helices in CDC13solution. 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 of1H‐nmr. Such a solution structure is consistent with the x‐ray crystal structure of one

ISSN:0006-3525    

DOI:10.1002/bip.360250107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have investigated CD spectra of double‐stranded RNA (dsRNA) in a variety of ethanolic and salt solutions. Solution conditions were varied by the addition of salts and ethanol, alone, or in combinations. (1) On addition of either salt or ethanol alone to solutions of dsRNA, we found that the positive CD band at 264 nm increased by up to 7% (in salt) or 12% (in ethanol) and underwent a long‐wavelength shift of 3 nm. Concomitantly, the negative CD band at 296 nm decreased. These CD changes may be indicative of an A‐ to A′‐RNA secondary‐conformation change on dehydration. (2) On addition of both salt and ethanol, in various combinations that caused precipitation of dsRNA, three types of CD spectral changes were found, which we take to indicate at least two different types of intermolecular arrays of RNA molecules. Type I precipitate was flocculent and its CD spectrum had a differential scattering component at long wavelengths. Type II condensate was finely dispersed and was characterized by a doubling of the CD magnitude at 264 nm and simultaneous disappearance of the 210 nm band, to give a CD spectrum close to that previously reported for RNA condensed in the presence of polyethylene glycol and salt [Ψ+RNA; Evdokimov, Y.M., Pyatigorskaya, T.L., Kadikov, V.A., Polyvtsev, O.F., Doskocil, J., Koudelka, J.&Varshavsky, Y.M., (1976)Nucleic Acids Res.3, 1533–1547]. Type III precipitate was flocculent and had CD spectra that included features that were present for Types I and II condensates; thus, the RNA in this precipitate may not have been in a unique interm

ISSN:0006-3525    

DOI:10.1002/bip.360250108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe enthalpies of transfer of proteins from aqueous solution to alcohol–water solutions are used as probes of solvent‐accessible surface for these proteins. Enthalpies of transfer to 10 wt% ethanol solutions are determined calorimetrically for the native proteins ribonuclease A, lysozyme, and ovalbumin. Ribonuclease A and lysozyme are reduced and carboxamidomethylated to produce configurations in which interior residues of the native protein are exposed to the solvent; enthalpies of transfer are determined for these species. These data are then compared with enthalpies of transfer for the constituent amino acids of the proteins. The enthalpies of transfer for the residues are used to generate a maximal enthalpy of transfer that can be compared with the enthalpies of transfer for the reduced, carboxamidomethylated proteins. The residue amino acid enthalpies are coupled with probabilities that each residue is an exterior residue to predict an enthalpy of transfer for the native protein that can be compared with the observed enthalpy. The probabilities developed by Wertz and Scheraga and Lee and Richards, and Chothia are then compared on their ability to predict the native enthalpies of transfer for the protein. The Wertz–Scheraga model gives the better fit of this data in all

ISSN:0006-3525    

DOI:10.1002/bip.360250109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe 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 × 105L/mol

ISSN:0006-3525    

DOI:10.1002/bip.360250110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractIturin A is a lipopeptide extracted from strains ofBacillus subtilis. Seven peptide residues form a cycle closed by a β‐amino acid carrying a hydrophobic tail. This compound is an antifungal and induces the formation of conducting pores in black lipid membranes. Two‐dimensional1H‐nmr was used for investigating its conformation in pyridine. A complete set of nuclear Overhauser effects (NOEs) was obtained from which interproton distances were deduced in a rather broad range of 2.2–4.2 Å. A special procedure was then used to optimize simultaneously experimental parameters and intramolecular energy calculated by semiempirical methods. A model of the conformation is proposed for the backbone for which there is an excellent coherence between NOEs, coupling constants, and intramolecular energy. The conformations of Asn, Gln, and Ser side chains appear to be much more flexible because of their interactions with the solvent. From this picture, iturin A seems to have a rather stiff ring surrounded by mobile side chains. Further studies of this lipopeptide and of other members of the family should enable us to approach some structure–activity relationships for this class of

ISSN:0006-3525    

DOI:10.1002/bip.360250111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY