摘要:

AbstractRandom copolymers ofL‐glutamic acid and ortho‐nitrobenzyl‐L‐glutamate were synthesized with different percentages of nitrobenzyl‐L‐glutamate, from 3 to 22%. These copolymers were studied by circular dichroism (CD) and potentiometric titrations in aqueous solutions in order to determine the variation of the stability of the secondary structure when the concentration of nitrobenzylglutamate varies in the copolymer. We observed that the stability increases with the concentration of glutamate. Such a stabilization could be due to either side‐chain interactions or interactions between the aromatic side chain with the backbone. An intermolecular aggregation was observed when the percentage of nitrobenzylglutamate was sufficently important, but such an aggregation may be avoided if a dioxane/water mixture is used

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151102

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

年代:1976

数据来源: WILEY

摘要:

AbstractA method is described for predicting and solving crystal structures of linear homopolysaccharides. The method is based on the refinement of the structure with respect to either stereochemical constraints or x‐ray diffraction intensities. In the refinement process, all conformational and packing features of the molecule, such as bond lengths, bond angles, conformational angles, nonbonded contacts, hydrogen bonds, etc., can be allowed to vary until the structure reaches both a conformation and crystalline packing that are in minimum disagreement with the stereochemical restraints and the diffraction data. In this fashion, both packing and conformational features of the structure can be simultaneously refined, and not separately as has been the custom in the past. The refinement procedure is based on a method of constrained optimization which possesses improved characteristics of reaching a solution and avoiding false minima, in comparison with least squares methods. The procedure is, in addition, capable of easily finding molecules of solvent of crystallization. The method was applied to further refining the previously solved crystal structure of V‐amylose. The results indicated that contrary to the previously found six‐fold molecular symmetry in the P212121space group, the V‐amylose molecule exhibits only two‐fold symmetry with the asymmetric unit consisting of three glucose residues in one‐half turn of the helix. The three residues are nonequivalent principally due to unequal rotational positions of the hydroxymethyl groups. The crystal structure of V‐amylose predicted from stereochemical refinement was identical in all details with that obtained from refining against X‐ray data. The excellent agreement with the diffraction data was indicated by the crystallographic disagreeme

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151103

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

年代:1976

数据来源: WILEY

摘要:

AbstractBy using the static correlations of fluctuations in the dihedral angles of the α‐helices of polyglycine and poly(L‐alanine) calculated previously, geometrical fluctuations of a section (consisting of up to 18 peptide units) of the α‐helices of infinite length are calculated. These fluctuations are found to differ in some respects (e.g., the dependence of amplitudes on the length of section) from those of a circular rod made of homogeneous continuous material. However, the moduli of the mechanical strengths (tensile Young's modulus, bending Young's modulus, and the shear modulus) of a circular rod are calculated, whose geometrical fluctuations are approximately equal to the fluctuations of a section consisting of 18 peptide units. They are of the order of 1011dyn/cm2. The tensile rigidity, flexural rigidity, and torsional rigidity are calculated to be 1.20 × 10−3dyn, 2.46 × 10−19dyn·cm2and 1.79 × 10−19dyn·cm2for polyglycine, and 1.96 × 10−3dyn, 4.05 × 10−19dyn·cm2and 3.28 × 10−19dyn·cm2for

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151104

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe Raman spectra of ovalbumin, ovomucoid, and conalbumin are reported. Spectral shifts in the conformationally sensitive amide I and amide III lines as a result of thermal denaturation indicate the formation of intermolecular β‐ sheets. A medium intensity line at 1260 cm−1in the spectra of ovomucoid and ribonuclease is demonstrated to contain a substantial contribution from tyrosine resi

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151105

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

年代:1976

数据来源: WILEY

摘要:

AbstractIn order to obtain information about the conformational features of a 2′‐O‐methylated polyribonucleotide at the nearest neighbor level, a detailed nuclear magnetic resonance study of AmpA was undertaken. AmpA was isolated from alkali hydrolysates of yeast RNA, and proton spectra were recorded at 100 MHz in the Fourier transform mode in D2O solutions, 0.01M, pH 5.4 and 1.5 at 25°C.31P spectra were recorded at 40.48 MHz. Complete, accurate sets of nmr parameters derived for each nucleotidyl unit by simulation iteration methods.The nmr data were translated into conformational parameters for all the bonds using procedures developed in earlier studies from these laboratories. It is shown that AmpA exists in aqueous solution with a flexible molecular framework, which shows preferences for certain orientations. The ribose rings exist as a2E⇄3Eequilibrium with the —pA ribose showing a bias for the3Epucker. The C(4′)—C(5′) bonds of both nucleotidyl units show significant preference (75–80%) to exist inggconformation. The dominant conformer (80%) about C(5′)—O(5′) of the 5′‐nucleotidyl unit isg′g′. Even though an unambiguous determination of the orientation of the 3′‐phosphate group cannot be made, tentative evidence shows that it preferentially occupiesg+domains [O(3′)—Ptransto C(3′)—C(2′)] in which the H(3′) —C(3′)—O(3′)—P(3′) dihedral angle is about 31°. There is reasonable evidence that the 2′‐O‐methyl preferentially occupies the domain in which the O(2′)—CH3bond istransto C(2′)—C(1′).Lowering of pH to 1.5, which results in protonation of both the adenine moieties, causes destacking of AmpA. Such destacking is accompanied by small, but real, perturbations in the conformations about most of the bonds in the backbone.A detailed comparison of the solution conformations of ApA and AmpA clearly shows that 2′‐O‐methylation strongly influences the conformational preference about the C(3′)—O(3′) bond of the 3′‐nucleotidyl unit, in addition to inducing small changes in the overall ribophosphate backbone conformational equilibria. The effect of 2′‐O‐methylation is such that the C(3′)—O(3′) is forced to occupy preferentially theg+domain rather than the normally preferredg−domain [O(3′)—Ptransto C(3′)—C(4′)] in ApA. The data on ApA and AmpA further reveal that the extent of stacking interaction is less in AmpA compared to ApA.It is suggested that stacked species of AmpA exist as right‐handed stacks where the magnitude of ω and ω′ about O(5′)—P and P—O(3′) is about 290°. The reason for the lesser degree of stacking in AmpA compared to ApA is intramolecular interaction between 2′‐O‐methyl and the flexible O(3′)—P—O(5′) bridge, the interaction causing some perturbation in the magnitudes of ω/ω′, causing destacking. The destacking will lead to an increase inχCNby a few degrees, causing an increase in2Epopulations; the latter in turn will shift the 3′ phosphate group from g−to g+domains. In short, a coupled series of conform

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151106

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe kinetics of γ‐benzyl‐L‐glutamate NCA's polymerizations in dioxane as solvent are discussed. The partial orders respective to [A], the NCA concentration and [I0], the initial initiator concentration are given; the rate constants are deduced and a mechanism is proposed to justify a rate of polymerizationVp=k[A][I0]2.The dependence of the rate constants on the conformation of the growing chains is demonstrated; the acceleration is attributed to the ordered structures favorable to hydrogen bonding. The kinetics of aging have also been examined and discussed; it is shown that they cannot modify the kinetics of polymerization.TheDPnwere obtained on the same samples before and after debenzylation; it is proved that at any concentration,DPn≃ [A0]/[I0].The molecular‐weight distributions were obtained by chromatography and a polydispersity lower than 1.3 was deduced for each sample. The trimodal distribution, appearing as soon as [A0]/[I0] is larger than 3, is attributed to the existence of the three structures σ, β, and α. The weight fraction of each of the structures was correlated to the kinetics of p

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151107

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

年代:1976

数据来源: WILEY

摘要:

AbstractSolutions of native collagen extracted from rat tail tendons in neutral salt solution have been studied by dynamic light scattering. The spectra obtained are consistent with the presence in solution of both single rod‐shaped collagen molecules and aggregates of molecules. No contribution to the spectrum has been detected at any scattering angle from rotational diffusion of single molecules, although a measurable broadening effect is expected at high angles. The translational diffusion coefficientDof single molecules, calculated from the broader spectral component, shows an anomalous dependence on collagen concentration with a maximum value ofD20,w= 8.6 ± 0.2 × 10−12m2/sec near the concentration 0.04% by weight. Above 0.05%Dfalls linearly with increasing concentration and takes the valueD20,w= 8.1 ± 0.2 × 10−12m2/sec at 0.064%

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151108

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe binding process between sodium poly(L‐glutamate) andtrans‐2,2′,2″,2‴‐tetrapyridyl‐Fe(III) complex ions in aqueous solution at pH around 7 has been studied by means of equilibrium dialysis and optical measurements. The binding isotherm indicates the occurrence of a cooperative process, whereby bound molecules facilitate the association of additional molecules. According to circular dichroism (CD) data, this effect is coupled with that which sees a conformational change in the charged polypeptide upon progessive binding of complex counterions. All these features are discussed in the light of the structural characteristics of the interacting species. A stereochemical model of the association “compl

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151109

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe conformational properties of poly(L‐p‐aminophenylalanine) have been investigated by potentiometric and circular dichroism (CD) techniques. It has been found that the polymer in the charge‐free state can assume two ordered conformations, depending upon temperature conditions. At room temperature the polymer assumes the right‐handed helical form by described Goodman and Peggion.1At temperatures higher than 40°C a new ordered conformation has been found, whose slow rate of formation and ir absorption properties are typical of the β‐structure. The thermodynamic parameters relative to the coil‐β transition, determined by potentiometric titration techniques, revealed that the thermodynamic stability of the β‐structure is mainly due to enthalpic factors. The formation of this structure is unfavored o

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151110

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

年代:1976

数据来源: WILEY

摘要:

AbstractPoly(Nε‐acetoacetyl‐L‐lysine), poly(Nδ‐acetoacetyl‐L‐ornithine) and poly(Nγ‐acetoacetyl‐L‐diaminobutyric acid) form colored complexes with ferric ions in water/dioxane solutions. These complexes are soluble at pH values lower than 2.8 and show their maximum absorption at 257 nm in the uv and at 478 nm in the visible region; whereas the ferric complex of the model compoundn‐hexylacetoacetamide exhibits absorptions centered at 258 and 536 nm, respectively. It is shown that in the complex of the model compound one metal ion is bound per acetoacetamide group, while in the complexes of the three polymers two β‐ketoamides side chains are bound per ferric ion under the same solvent, pH, concentration, and ionic strength conditions. The binding constants of ferric ions to the three polymers, and the formation constant of the ferric complex of the model co

ISSN:0006-3525    

DOI:10.1002/bip.1976.360151111

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

年代:1976

数据来源: WILEY