摘要:

AbstractFourier transform ir attenuated total reflectance (FTIR ATR) spectra have been obtained to investigate the secondary structure of poly(γ ‐methylL‐glutamate) (PMLG) surfaces untreated and treated with formic acid in a quantitative manner. Curve analysis including Fourier self‐deconvolution and the band fitting was applied to the ir spectra in the amide II region, revealing that the amide II band of those surfaces consists of five components. The essentially α‐helical form in the PMLG surface layer transformed readily into the β‐structure by the formic acid treatment, and the β‐structure content increased with increasing time of the treatment. The content of random coil structure of treated PMLG was generally very little and/or negligible. The depth profile obtained by considering the depth of ir beam penetration indicated that the β‐structure content also increased with approaching the

ISSN:0006-3525    

DOI:10.1002/bip.360320302

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

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral harmonic models of protein fluctuations are used to calculate the heat capacity. They get the spectral density of conformational modes from inelastic neutron scattering, normal mode calculations, or macroscopic elasticity (Debye model). It is assumed that the low‐frequency spectral density depends only weakly on temperature and protein species. The Debye model predicts temperatures below which modes are primarily in their ground states: 10 and 80 K for the lattice and conformational modes, respectively. The models differ most below 100 K. The mode calculations yield the most accurate predictions, though all three models are within twofold of the data. The heat capacity has the power law formaTbforT<30 K. The experimentalb's of proteins are 1.6–1.8, and the theoretical, 1.1–1.3. One possible explanation for the discrepancy is the occurrence of transitions between discrete conformations. All of the models approach the measured data in the range 100–200 K. They are very similar above 200 K, where the heat capacity includes significant contributions from bond stretching and bending. This masks the possible anharmonic behavior of the conformational modes. Hydration substantially increases the heat capacity above 200 K. This effect seems to be a consequence of conformational transitions that have higher energy than the ones seen with low hydration. The analysis also predicts that denaturation with constant hydration produces a negligible increase of heat capacity. The larger increment in solution arises from the different hydration of the folded and unfolded states, and is responsible for the existence of cold denaturation. This phenomenon is thus predicted not to occur when the hydration is c

ISSN:0006-3525    

DOI:10.1002/bip.360320303

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

年代:1992

数据来源: WILEY

摘要:

AbstractUsing polyethylene glycol and dextran as osmotic stressing agents, the concentrations of hyaluronate and heparin were measured as a function of osmotic pressure II over the range of 0.03 to nearly 50 atmospheres. The experimental results were analyzed in terms of the Donnan osmotic pressure, the virial expansion, and Flory's first neighbor interaction parameter. In addition, II was looked at as a function of the reciprocal cube root of the concentration, which represents an average intermonomer spacing at high concentrations. The decay lengths in the so‐called hydration region were found to be around 2.6 Å and negligibly salt dependent. In the electrostatically dominated region the decay lengths were found to be dependent on the ionic strength, but not simply so. The osmotic compressibilities were also calculated, and were compared to compressibility data of corneal stroma and articular cartilage. These latter compressibilities were close to those for the pure hyaluronate and heparin, strengthening the evidence that glycosaminoglycans (GAGs) are largely responsible for connective tissue compressibility. Higher compressibilities for previously reported GAG data is thought to be related to the protein content of those sampl

ISSN:0006-3525    

DOI:10.1002/bip.360320304

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe amide II vibrational CD (VCD) spectra of poly(L‐glutamic acid) and poly(L‐lysine) in various conformational forms and those of several proteins in H2O have been measured. Characteristic VCD patterns have been observed in the amide II region due to helix, β‐sheet, and coil conformations in polypeptides. Based on their x‐ray crystal structures, the proteins studied have been assigned to six categories. Proteins in the same category give rise to similar amide II VCD. While the protein conformational type is indicated using the amide II VCD, discrimination between types is less characteristic than with the previously studied amide I' VC

ISSN:0006-3525    

DOI:10.1002/bip.360320305

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe preferred conformations of ribo and deoxyribo α‐nucleosides and β‐nucleotides, the stereoisomers of the naturally occurring β‐isomers, are worked out by minimizing the conformational energy as a function of all the major parameters including the sugar ring conformations along the pseudorotation path. The results of the studies bring out certain distinct conformational features that are at variance with their β counterparts. The range of glycosyl conformations are found to be not only quite restricted here but favor predominantly theanticonformation. Thesynglycosyl conformation for the entire region of α values are found to be energetically less favorable, with the barrier toanti⇆syninterconversion being higher especially in α‐ribonucleosides. The energetically preferred range of pseudorotation phase angles (P) is also considerably restricted andPvalues corresponding to the C1′‐exorange of sugars are highly unfavorable for α‐nucleosides, in sharp contrast to the broad range of sugar ring conformations favored by β‐isomers. While bothtrans ≃180° andskew ≃270° conformations around the C3′‐O3′ (ϕ′) bond are favored for β‐3′‐nucleotides with deoxyribose sugars, ribose sugars seem to favor only theskewvalues of ϕ′. Most interestingly and in sharp contrast to β‐stereoisomers, an energy barrier is encountered at P values corresponding to O4′‐endosugars. This suggests that the possible sugar pucker interconversion between C2′‐endo/C3′‐exoand C3′‐endo/C2′‐exoin a‐anomers could take place only through the O4′‐exoregion. Likewise the possible path ofanti⇆syninterconversion in α‐nucleosides is not via highanti, in sharp contrast to α‐nucleosides. These observations should be borne in mind while assigning the sugar ring conformers in α‐nucleosides and those containing them from nmr investigations. Comparison of the results with α‐anomers seem to suggest on the whole a lack of conformational variability or the restricted nature of α‐stereoisomers

ISSN:0006-3525    

DOI:10.1002/bip.360320306

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn previous work, it was shown that poly [d(AC) · d(GT)] could be forced into the Z form by strong dehydrating conditions, provided EDTA was not present. Presumably multivalent impurities were also necessary for the transition. In order to gain control over the B to Z transition for this DNA, we carefully removed all divalent contaminants from the sample and asked the obvious question: What ions are necessary for the transition under dehydrating conditions? We systematically investigated the effect of various multivalent ions. The common contaminants Ca2+, Mg2+, and Fe3+will not cause the transition, but Co2+and Ni2+facilitate the transition, undoubtedly because of their well‐known propensity to bind to purine N7. Since the transition also depends on the synergistic dehydrating action of sodium perchlorate and ethanol, we include CD spectra for the independent variations of these two factors. In addition, vacuum‐uv CD spectra for the A form and various B forms of poly [d (AC) · d (GT)] are presented for the first

ISSN:0006-3525    

DOI:10.1002/bip.360320307

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

年代:1992

数据来源: WILEY

摘要:

AbstractTo probe differences in conformation of the type 1 and type 2 linkages in blood group oligosaccharides, two‐dimensional nuclear Overhauser effect spectroscopy (2D‐NOESY) and1H T1data were obtained for two blood group A oligosaccharide alditols containing the type 1 and type 2 linkage. The NOE data were interpreted using a complete relaxation matrix approach. Simulations of NOE and T1values were made using disaccharide and tetrasaccharide model conformations generated by a systematic variation of the glycosidic dihedral angles ϕ and ψ. NOEs from the amide protons of GlcNAc and GalNAc in the type 1 pentasaccharide alditol were obtained, and simulated in a manner similar to those from carbon‐bound protons. In addition to providing data for determining the conformation of the type 1 linkage from amide proton NOEs of GlcNAc and GalNAc to neighboring residues, amide proton NOEs also yield information on the orientation of the acetamido side chains. The amide NOE data indicated subtle differences in the orientation of the amide side chain of GlcNAc among the A type 1 pentasaccharide alditol and two previously studied blood group oligosaccharides, lacto‐N‐difucohexaose 1 and lacto‐N‐fucopentaose 1. From the NOE and1H T1data, and from simple rigid geometry energy calculations, it is concluded that the type 1 and type 2 linkages in the oligosaccharides studied have different conformations and that these conformations are relatively ri

ISSN:0006-3525    

DOI:10.1002/bip.360320308

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

年代:1992

数据来源: WILEY

摘要:

AbstractWe have examined intramolecular hydrogen bonding in four homologous compounds, N‐acetyl‐, N‐propionyl‐, N‐i‐butyryl‐, and N‐pivaloyl‐proline‐methylamide, in methylene chloride, by means of1H‐nmr and ir measurements. At room temperature, the majortransconformer of MeCO‐Pro‐NHMe appears to be approximately 68% intramolecularly hydrogen bonded, thetransconformers of EtCO‐Pro‐NHMe and i‐PrCO‐Pro‐NHMe are approximately 75% intramolecularly hydrogen bonded, andt‐BuCO‐Pro‐NHMe is approximately 50% intramolecularly hydrogen bonded. Thus, the internally hydrogen‐bonded state (C7or γ‐turn) is significantly less populated for the N‐pivaloyl compound than for the other three molecules in this series. Variable temperature measurements indicate that for each proline derivative there is very little enthalpic difference between the intramolecularly hydrogen‐bonded and nonhydrogen bonded states of thetransrotamer. Changing the N‐terminal acyl group also affects intramolecular hydrogen bonding (including

ISSN:0006-3525    

DOI:10.1002/bip.360320309

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

年代:1992

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360320310

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

年代:1992

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360320301

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

年代:1992

数据来源: WILEY