摘要:

Abstract13C‐nmr spectroscopy was used to determine the location of the structured segment of the chain of histone H1 in water and NaCl solutions. The segment found (41–89) is contained in the area proposed by others on the basis of1H‐nmr studies. The number of basic groups left in the mobile ends of the protein matches the number of bases of internucleosoma

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180102

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe synthesis and characterization of the block copolypeptide (Leu67, Lys33)100Orn20, a synthetic model of histone, are reported. In neutral aqueous solutions, 80% of the etheropolypeptide block assumes an α‐helical conformation, whereas the polyornithine block is in a random‐coil conformation. In the association complexes with DNA, melting and titration experiments, as well as CD results, indicate that the polyornithine block interacts with DNA, whereas at least 2/3 of the lysine residues of the (Leu, Lys) moiety are excluded from the direct binding with DNA. CD spectra of the association complexes reveal significant differences from those obtained with DNA–polyornithine and DNA–polylysine complexes but substantial similarities with CD spectra of native and reconstituted nucleohistones. In contrast to DNA–polyornithine complexes, the CD spectra of the ternary complexes, copolypeptide–DNA–ethidium bromide, indicate a strong reduction of the dye intercalation. The low‐angle x‐ray diffraction pattern, reminiscent of that of chromatin, reveals the presence of a superstructure in these complexes. The results obtained are discussed in connection with the expected structural fea

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180103

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe complex dielectric constant of collagen in aqueous solutions (polymer concentration,Cp= 0.02–0.2%) was measured at 10°C in the frequency range from 3 Hz to 30 kHz. The loss peak forCp= 0.02% is located at 90 Hz and the dielectric relaxation time τDis estimated to be 1.8 ± 0.3 msec. The τDagrees well with the rotational relaxation time estimated from the reduced viscosity, and the relaxation is ascribed to the end‐over‐end rotation of the molecule. TheCpdependence of τDand the dielectric increment Δε are interpreted in terms of the aggregation of molecules. The dipole moment of a molecule, obtained from Δε atCp= 0.02% and pH 6.5, is (5.2 ± 0.2) × 104D, which is explained by the asymmetrical distribution of the ionized side chains

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180104

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

年代:1979

数据来源: WILEY

摘要:

AbstractDielectric measurements have been carried out on partially hydrated collagen in the frequency ranges 100 kHz–5 MHz, 100 MHz–1 GHz, and 8–23 GHz. In the low‐frequency range, a dispersion was observed around 100 kHz which results from inhomogeneous conductivity of the samples. A dielectric relaxation was observed aroud 0.3 GHz using time‐domain‐spectroscopy techniques. This relaxation can be considered to originate from mobile side chains. Microwave measurements indicate that the water relaxation may extend into the 10‐GHz region. An apparent discrepancy between the main water relaxation time and the average rotational correlation time of water as measured by nmr line widths was resolved by the assumption that a fraction of the water molecules is bound to the collagen with residence times on the order of 10−6sec, whereas the remainder of the water is only weakly bound and exhibits rotational rates on the or

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180105

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

年代:1979

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance and dielectric data on hydrated collagen are interpreted in terms of Ramachandran's hydration model. It is found that all data are compatible with this model, indicating two specific binding sites per three amino acids in the threefold collagen helix. Sorption data have been interpreted according to the multilayer theory of Guggenheim and used to derive the fraction of bound water in the primary sites. From magnetic resonance anisotropies structural details of the position of the water molecules can be derived under the assumption that both sites are equally occupied. The residence time of a water molecule in one of these sites in moderately hydrated collagen (45 g H2O/100 g collagen) is 1.2 × 10−6sec. The remainder of the water is weakly bound and consists of rapidly exchanging species with rotational correlation time shorter than 10−10sec. The sites are 50% occupied at a water content of 10 g/100 g collagen and may contribute significantly to the stability of the collagen threefold h

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180106

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

年代:1979

数据来源: WILEY

摘要:

AbstractMeasurements of the intrinsic viscosity of the urease “monomer” and of a mixture of oligomers are shown to lead to the conclusion that urease oligomerizes in a linear fashion, when viewed in the light of several available theories of intrinsic viscosity of rigid protein macromolecules. This conclusion is also consistent with previously reported work on the sedimentation coefficients of the urease oligomers. The use of a detailed subunit structure for the urease “monomer” and oligomers is explored and found to give quantitatively good results for all hydrodynamic properties of all urease oligomers. The realm of validity of the intrinsic viscosity theories proposed by Garcia de la Torre and Bloomfield, by Tsuda, and by Abdel‐Khalik and Bird is explored in thi

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180107

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

年代:1979

数据来源: WILEY

摘要:

AbstractBy generating classes of random structures for trypsin inhibitor and carp myogen, each consistent with a given set of experimental or theoretical information, we have assessed the relative utility of various experiments and theories in deducing the conformation of macromolecules. We compare the calculated structures with known x‐ray coordinates and compute for each class an average error. Small errors mean that the experimental or theoretical constraints limit the structures to the vicinity of the crystal structure, whereas large errors show that the constraints permit a wide variety of tertiary conformations. We find the following points to hold true: (1) Qualitative information on all the distances, as might be obtained from the correct prediction of interresidue contacts, effectively determines the structure (error approximately 1 Å). (2) Quantitative information on a limited number of distances, as might be obtained from nmr or crosslinking experiments, significantly restricts the range of possible structures only when the number of distances given is comparable to the number of residues (error approximately 3 Å). (3) Quantitative information on the distances of each residue to the center of mass of the molecule, as might in part be obtained from solvent accessibility and solution x‐ray studies, is not particularly restrictive by itself (error approximately 5 Å). (4) Complete qualitative local distance information, as might be obtained from secondary prediction and CD/ORD studies, is clearly consistent with a wide variety of tertiary structures (error approximatel

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180108

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

年代:1979

数据来源: WILEY

摘要:

AbstractA model for the time dependence of DNA conformational state probabilities is formulated in the form of first‐order differential equations. This model is applied to investigate the renaturation and denaturation rates for T2 and T7 DNA as reported in the series of experiments by Record and Zimm. Qualitative agreement is found in denaturation and for series of renaturation experiments with the same initial condition. However, partial agreement with series of renaturation experiments having the same final condition is obtained only by including an initial bimolecular step with properly matched pairs of strands. Comparison of all experiments with the calculated rates yields 5 × 104min−1as the step rate for melting a single base

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180109

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe local electrostatic order in polyelectrolytic solutions has been studied by magnetic birefringence measurements on short segments (n∼ 34) of the (Tyr‐Glu)npolypeptide in high magnetic fields up to 13 T. We give evidence that only above a critical polymer concentration do small domains exist within which the polymers show a parallel ordering. This structural order disappears suddenly at ionic strengths above about 5 × 10−2Mand above a melting temperature of abou

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180110

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

年代:1979

数据来源: WILEY

摘要:

AbstractStatistical mechanical averages of vectors and tensors characterizing the allowed configurations of randomly coiling polynucleotides have been calculated for chains of 20–210repeating units. Specifically, the persistence vectorp= 〈r〉 has been obtained as a function of chain length. Configurational averages of the Cartesian tensors formed from the displacement vector ρ =r–phave been computed up to and including the tensor of seventh rank. From these tensors the three‐dimensional spatial distributions of end‐to‐end vectors have been constructed to provide comprehensive pictures of the directional tendencies of the randomly coiling polynucleotide. The elements of the third and fourth moment tensors, however, give sufficient information to represent accurately the qualitative features of the spatial distributions. For long chains, more than 26(64) repeating units, the spatial distributions assume spherically symmetric shapes that can be adequately characterized by one‐dimensional radial distribution functions. These radial distribution functions agree well with the radial distributions calculated from Monte Carlo samples containing more than 5000 chains. The constraints of fixed bond lengths, fixed bond angles, and hindered internal rotations severely distort the spatial distributions of short polynucleotide chains to mushroom‐shaped volumes. These skewed distributions provide information useful to the analysis of small, single‐stranded loops, bulges, and circles. The formation of these structures requires the termini of the polynucleotides to lie within specifically delineated volumes with respect to coordinate systems affixed to the first bonds of the chains. The extent to which these loop closure volumes overlap the three‐dimensional spatial distributions provides estimates of loop formation that are much more reliable than earlier studies based upon the radial

ISSN:0006-3525    

DOI:10.1002/bip.1979.360180111

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

年代:1979

数据来源: WILEY