ISSN:0006-3525    

DOI:10.1002/bip.360230602

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe conformation of heparin in water was investigated by intermediate‐angle x‐ray scattering (IAXS). The theoretical scattering function for the coil conformation was calculated by the Monte Carlo method using the approximation of separable conformation energies and the conformation energies computed for two disaccharide pairs in heparin. From x‐ray scattering in a relatively small‐angle region, the conformation of heparin is not the ordered 21helix conformation but the coil conformation obtained by the Monte Carlo calculation. It is expected, from x‐ray scattering in a relatively wide‐angel region, that the sulfate groups of heparin maintain about 7 Å

ISSN:0006-3525    

DOI:10.1002/bip.360230603

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe rate of deuterium exchange of the 8‐CH group in a purinedeoxyribonucleotide, is the same as the 8‐CH exchange rate in the corresponding purineribonucleotide, with the exception of 5′‐nucleotides of guanine. The observed 20% slower rate of 8‐CH exchange in 5′‐dGMP versus 5′‐rGMP, over the temperature range 50–80°C, are attributable to differences in molecular conformation, including differences in ring puckering of the furanose substituents. Minor differences in 8‐CH exhange rates are observed between 5′‐and cyclic (3′:5′)‐deoxyribonucleotides of a given purine, which are similar to those observed previously between corresponding 5′‐ and cyclic ribonucleotides that have been attributed to the charge difference of their respective phosphate groups [Ferreira, S. A.&Thomas, G. J., Jr. (1981)J. Raman Spectrosc.11, 508–514]. The coupling of guanine and furanose ring structures in the 5′‐nucleotides is also evident from the vibrational frequencies of the guanine ring, which are strongly dependent on the pucker of the attached furanose moiety. Raman difference spectroscopy clearly reveals the dependence of purine nucleotide spectra on sugar‐ring pucker. In the case of GMP, the guanine characteristic ring breathing mode near 600–700 cm−1depends for its exact position and intensity on the proportion of C3′‐endo(668 cm−1) and C2′‐endo(682 cm−1) conformers in equilibrium with one another. The Raman intensity ratioI(668)/I(682) is proposed as a measure of the conformer ratio C3′‐endo/C2′‐endoin 5′‐dGMP with possible application also to nucleic acids. Among cyclic nucleotides, differences in spectra of deoxyribo‐ and ribo

ISSN:0006-3525    

DOI:10.1002/bip.360230604

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe report the crystal‐structure analysis of a complex involving the drug proflavine and the two dinucleoside monophosphates cytidylyl‐3′,5′‐adenosine (CpA) and uridylyl‐3′,5′‐guanosine (UpG). The planar drug molecule is intercalated between C ⃛G and U ⃛A Watson‐Crick base pairs, in a double‐helical fragmentlike arrangement. Sugar conformations at the 3′‐ends of the two strands are dissimilar. The backbone conformations fall within the ranges of values noted previously for dinucleoside intercalation complexes, and some correlations involving these are noted. The separation of the two strands and the basic twist angle of 16°, compared to other reported complexes, are indicative of sequence‐depen

ISSN:0006-3525    

DOI:10.1002/bip.360230605

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe fluorescence polarization method was applied to the investigation of the micro‐Brownian motion of amylose chains having a wide range of degree of polymerization (DP). We prepared two types of fluorescent conjugates of amylose: amylose conjugated with fluorescein randomly throughout the chain (F‐amylose) and amylose conjugated locally on a terminal segment (t‐F‐amylose). The degree of fluorescence polarization of these conjugates was measured by changing the solvent viscosity at a constant temperature (25°C). The data obtained were analyzed by a Perrin‐type equation to calculate the mean rotational relaxation time, 〈ρ〉. By examination of the plots of 〈ρ〉 vs DP, and by comparison of 〈ρ〉 with the theoretical rotational relaxation time of the whole molecule at a given DP, it was found that 〈ρ〉 mainly reflects the segmental motion of the amylose chain in the high‐DP range. Thus, the fact that 〈ρ〉 for t‐F‐amylose is much smaller than that for F‐amylose at a sufficiently high DP shows that a terminal segment undergoes a more rapid micro‐Brownian motion than interior segments. In the low‐DP range, we felt that the rotational diffusion of the whole molecule contributes significantly to the relaxation process. We also examined, for comparison, the segmental motion of dextran and pullulan in a similar manner and found that these segmental motions are more rapid than those of amylose. Based on the results obtained, the segmental mobility and conformation of the amylose molecul

ISSN:0006-3525    

DOI:10.1002/bip.360230606

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

年代:1984

数据来源: WILEY

摘要:

AbstractHelical hydrophobic moment ratios, 〈h2〉/〈H2〉, have been evaluated for 34 polypeptides under conditions where the helix content is dictated solely by the short‐range interactions operative in aqueous media. The mean‐square helical hydrophobic moment is denoted by 〈h2〉, and 〈H2〉 is the averaged of the squared hydrophobicites. This ratio would be one in absence of any correlation in the hydrophobicities of amino acid residues in helices. The 〈h2〉/〈H2〉 tend to be substantially larger than values of the analogous ratio formulated for the mean‐square dipole moments of typical synthetic polymers. For 24 of the 34 polypeptide chains considered, 〈h2〉/〈H2〉 is found to be greater than one, indicating a tendency to form helices with amphiphilic character. The ratio is exceptionally large in the case of the δ‐hemolysins. It is also large for two other surface‐active peptides, for two of the four apolipoproteins examined, and for myohemerythrin. A much smaller 〈h2〉/〈H2〉 is found for melittins. If melittins is to form helices with large 〈h2〉/〈H2〉, the configurational statistics must be governed by effects in addition to those sho

ISSN:0006-3525    

DOI:10.1002/bip.360230607

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

年代:1984

数据来源: WILEY

摘要:

AbstractTwo photoaffinity analogs of ethidium, 8‐azido‐3‐amino, and 3‐azido‐8‐amino‐5‐ethyl‐6‐phenylphenanthridinium chloride, have been used to probe the structure of mammalian chromatin and its interactions with the ethidium moiety. The monoazido analogs were established as suitable probes by comparing their interactions with chromatin and pure DNA prepared from chromatin to those of the parent ethidium bromide. Scatchard analysis of the binding data determined from spectrophotometric titrations showed that the analogs interacted with both nucleic acids in a manner similar to the parent compound. The effect of chromatin proteins on the interaction of the ethidium moiety with intact chromatin was investigated directly. By exposing the noncovalent complex to visible light, the monoazido analog was attached covalently in its interaction sites within chromatin, and the amount of drug bound covalently to DNA was determined for both protein‐free DNA and chromatin. Using saturating concentrations of drug, DNA within intact chromatin was found to be associated with only half as much drug as DNA extracted from its protein prior to drug exposure. The distribution of drug bound within chromatin was determined following the attachment of the monoazido analog (by photoactivation) to chromatin that had undergone limited nuclease digestion. Several distinct populations isolated by size fractionation and quantitative measurements revealed that (1) both the core particles and the spacer‐containing particles contained bound drug, reflecting high‐affinity binding sites; and (2) chromatin particles containing 150 DNA base pairs (putatively nucleosome core structures) contained less total bound drug at high drug concentrations than those particles

ISSN:0006-3525    

DOI:10.1002/bip.360230608

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

年代:1984

数据来源: WILEY

摘要:

AbstractOligomeric cyclic disulfides, obtained by mild oxidation of the fully protected dipeptideL‐cysteinyl‐L‐cysteine, have been isolated by gel and thin‐layer chromatography. Polymeric material was recycled by a thiol–disulfide exchange‐reaction performed at basic pH. Spectroscopic investigations of the monomer and the two dimers indicate that conformers characterized by dihedral angles about the SS bond close to ±90° are preferred. Moreover, chiroptical and1H‐nmr data for these compounds suggest higher mobility for the two dimers. The antiparallel dimeric disulfide can be considered a model compound for the hinge region formed at the subunit interface of the bovine seminal ribonuclease, a dimeric enzyme showing a complex

ISSN:0006-3525    

DOI:10.1002/bip.360230609

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

年代:1984

数据来源: WILEY

摘要:

AbstractA quasi‐harmonic approximation is described for studying very low frequency vibrations and flexible paths in proteins. The force constants of the empirical potential function are quadratic approximations to the potentials of mean force; they are evaluated from a molecular dynamics simulation of a protein based on a detailed anharmonic potential. The method is used to identify very low frequency (∼1 cm−1) normal modes for the protein pancreatic trypsin inhibitor. A simplified model for the protein is used, for which each residue is represented by a single interaction center. The quasi‐harmonic force constants of the virtual internal coordinates are evaluated and the normal‐mode frequencies and eigenvectors are obtained. Conformations corresponding to distortions along selected low‐frequency modes a

ISSN:0006-3525    

DOI:10.1002/bip.360230610

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

年代:1984

数据来源: WILEY

摘要:

AbstractPolarized dynamic light‐scattering measurements on superhelical pBR322‐plasmid DNA solutions in 0.2MNaCl, 2 mMNaPi, pH 7.0, 2 mMEDTA result in a translational diffusion coefficientD T,20°C0= (3.77 ± 0.10) × 10−8cm2/s for the native molecule. Modeling the DNA, in the simplest approximation, as a 10 × 440‐nm effective hydrodynamic rigid rod yields a good fit to the apparent diffusion coefficient angular‐dependence data up to 70°; the model fails at higher angles, probably due to the effects of flexibility or branching of the rod. Diffusion coefficient titration experiments with a platinum complex intercalating agent (PtTS) result in a titratable superhelix density ofσ= −0.079 ± 0.008 under our experimental conditions, corresponding to about 34 superhelical turns in the native DNA. The DNA contour length predicted by our two independent results, the rod dimensions and the number of superhelical turns, is in excellent agreement with the contour length calculated from the number of base pairs, supporting the hydrodynamic approximation of an effective rodlike structure for this small DNA

ISSN:0006-3525    

DOI:10.1002/bip.360230611

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

年代:1984

数据来源: WILEY