摘要:

AbstractThe electric birefringence of restriction enzyme fragments of DNA has been investigated as a function of DNA concentration, buffer concentration, and molecular weight, covering a molecular weight range from 80 to 4364 base pairs (bp) (6 × 104–3 × 106daltons). The specific birefringence of the DNA fragments is independent of DNA concentration below 20 μg DNA/ml, but decreases with increasing buffer concentration, or conductivity, of the solvent. At sufficiently low field strengths, the Kerr law is obeyed for all fragments. The electric field at which the Kerr law ends is inversely proportional to molecular weight. In the Kerr law region the rise of the birefringence is accurately symmetrical with the decay for fragments ≤ 389 bp, indicating an induced dipole orientation mechanism. The optical factor calculated from a 1/Eextrapolation of the high field birefringence data is −0.028, independent of molecular weight; if a 1/E2extrapolation is used, the optical factor is −0.023. The induced polarizability, calculated from the Kerr constant and the optical factor, is proportional to the square of the length of the DNA fragments, and inversely proportional to temperature. Saturation curves for DNA fragments ≤ 161 bp can be described by theoretical saturation curves for induced dipole orientation. The saturation curves of larger fragments are broadened, because of a polarization term which is approximately linear inE, possibly related to the saturation of the induced dipole in high electric fields. This “saturated induced dipole” is found to be 6400 D, independent of molecular weight. The melting temperature of a 216‐bp sample is decreased 6°C in an electric field of 8 kV/cm, because the lower charge density of the coil form of DNA makes it more stable in an electric field

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200302

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe interaction of the fluorinated antimalarial drug fluoroquine [7‐fluoro‐4‐(diethyl‐amino‐1‐methylbutylamino)quinoline] with DNA, tRNA, and poly(A) has been investigated by optical absorption, fluorescence, and19F‐nmr chemical‐shift and relaxation methods. Optical absorption and fluorescence experiments indicate that fluoroquine binds to nucleic acids in a similar manner to that of its well‐known analog chloroquine. At low drug‐to‐base pair ratios, binding of both drugs appears to be random. Fluoroquine and chloroquine also elevate the melting temperature (Tm) of DNA to a comparable extent. Binding of fluoroquine to DNA, tRNA, or poly(A) results in a downfield shift of about 1.5 ppm for the19F‐nmr resonance. The chemical shift of free fluoroquine depends on the isotopic composition of the solvent (D2O vs H2O). The solvent isotope shift is virtually eliminated by fluoroquine binding to any one of the nucleic acids.19F‐nmr relaxation experiments were carried out to measure the spin‐lattice relaxation time (T1),19F{1H} nuclear Overhauser effect (NOE), off‐resonance intensity ratio (R), off‐resonance rotating‐frame spin‐lattice relaxation time (T 1ρoff), and linewidth for fluoroquine in the nucleic acid complexes. By accounting for intramolecular proton‐fluorine dipolar and chemical‐shift anisotropy contributions to the fluorine relaxation, all of the relaxation parameters for the fluoroquine–DNA complex can be well described by a motional model incorporating long‐range DNA bending on the order of a microsecond and an internal motion of the drug on the order of a nanosecond. Selective NOE experiments indicate that the fluorine in the drug is near the ribose protons in the RNA complexes, but not in the DNA complex. Details of the binding evidently differ for the two types of nucleic acids. This study provides the foundation for a

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200303

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

年代:1981

数据来源: WILEY

摘要:

AbstractA technique for the measurement of the dynamic Young's modulusEand logarithmic decrement

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200304

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe structures of viral φ29 DNA condensed by triamines, principally spermidine, in 10−3MNaCl were investigated by static and dynamic light scattering and electron microscopy. All of the results for DNA condensed in 30 μMspermidine at neutral pH are quantitatively consistent with a toroidal structure with a mean outer diameter of 1850 Å. At pH 10.2, however, condensed structures of a completely different size and shape are observed for the first time. These structures are also more irregular in shape and more polydisperse than those at neutral pH. This conformational change is believed to result from a change in the mode of spermidine binding that is coupled to, or associated with, the (premature) titration of protons on the base‐ring nitrogens of guanine and thymine. Besides spermidine, certain homologs of spermidine, in which the butyl moiety of spermidine was replaced by longer pentyl through octyl moieties, were also studied. Though all of the triamines condensed the DNA at 30 μM, aggregation became a more prevalent occurrence as the length of the end chain increased. This suggests that crosslinking may play an important role in the condensation process. Finally, these aggregates are dissociated to a considerable extent at pH 10.2, and the resulting compact structures appear to be quite similar, independent of the triamine used to condense the DNA. The observed partial breakdown of aggregates is also consistent with the hypothesis of a change in mode of triamine binding at

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200305

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

年代:1981

数据来源: WILEY

摘要:

AbstractIn order to investigate the contribution from the chiral penultimate unit to the enantiomer selection in the activatedN‐carboxyanhydride (NCA) polymerizations, the addition reaction toN‐[(S)‐methylbenzyl]glycine NCA of various α‐amino acid hydantoins activated by the tertiary amines was investigated in different solvents. The reactions of activated Ala, Val, and Phe hydantoins were stereoselective and suggested the participation of the penultimate unit in the enantiomer selection of the activated NCA type of polymerization. The degree of enantiomer selection was not well correlated with the structure of hydantoins. Taking into account the dipole repulsion and the orbital overlapping between the reaction species, the transition‐state model was proposed, which gave a good explanation of the selectivity for (R)‐hydantoin in PhNO2and CH3CN and the selectivity for (S)‐hydantoin in AcNMe2and HCONMe2. In these two types of solvents the orientation of the methylbenzyl group with respect to the NCA ring is so different that the direction of the approach of the activated hydantoin to the NCA is different. This difference leads to the inversion of enantiomer selection in amide solvents and in others. Cationic species derived from tertiary amines and the chiral amide compound were found to affect the enantiomer selection in the model reaction. The implications of these findings with regard to enantiomer selection in the activated NCA type of polymerization

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200306

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

年代:1981

数据来源: WILEY

摘要:

AbstractAs a model compound for the growing chain in the activated‐NCA type of polymerization of α‐amino acidN‐carboxyanhydride (NCA), 3‐[ω‐acetylglycyl‐poly(α‐amino acid) acyl]‐α‐amino acid NCA (called the prepolymer) having various degrees of polymerization (DPs) was synthesized by the polymerization of Phe, Val, Glu(OEt), and Asp(OBzl) NCA in the presence of AcGly NCA by the tertiary amine. Activated (S)‐Phe, Val, Glu(OEt), and Asp(OBzl) NCA were added to the terminal cyclic group of the corresponding (S)‐ or (R)‐ prepolymer, and the enantiomer selectivity in the reaction was investigated. With prepolymers having DPs ranging from 1 to 15, the addition reaction always took place preferentially between species having the same configuration, and the degree of the enantiomer selection increased with increasing DP of the prepolymer. With prepolymers having DP = 1 and 2, we found contributions from the chiral terminal unit and the chiral penultimate unit to the enantiomer selection, respectively. Prepolymer having DP = 5 was shown to take a β‐type conformation, which led to higher enantiomer selection; and prepolymers having DP = 10 and 15 were shown to take an α‐helix conformation, which led to much higher enantiomer selection than did the β‐type conformation. In the present investigation the mechanisms of terminal‐unit control, penultimate‐unit control and conformational control of the enantiomer selection in the activated‐NCA ty

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200307

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

年代:1981

数据来源: WILEY

摘要:

AbstractA theory explicitly allowing the possibility of aggregation of multistrand biopolymers is proposed. It is found that the same secondary bonds responsible for stabilizing the native structure at low temperature will promote aggregation in the thermal denaturation region for sufficiently long chains. A requirement for both open and zippered regions dictates that the aggregation region does not extend far belowTm. However, its width, or extension on the high‐temperature side ofTm, is a strongly increasing function of chain length and also of the cooperativity parameter. The present theoretical results obtained for DNA and collagen with almost no adjustable parameters are in good qualitative agreement with a number of previously poorly understood experimental observations. The significance of such a spontaneous aggregation phenomenon for genetic recombination is note

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200308

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

年代:1981

数据来源: WILEY

摘要:

AbstractMonte Carlo simulations are reported for a system of 447 water molecules enclosing a B‐DNA double‐helix fragment with 12 base pairs and the corresponding sugar and phosphate units. From a detailed analysis on the interaction energies and probability distributions (at a simulated temperature of 300 K), the water molecules can be partitioned into clusters strongly interacting with (1) the phosphates, (2) the sugars, (3) the sugarsandthe bases, and (4) the base pairs. In addition,transgrooveandinterphosphatefilament of hydrogen‐bonded water molecules have been detected. From simulations performed with variable numbers of water molecules, a theoretical isotherm has been obtained, with the characteristic sigmoidal shape, known from absorption–desorption experiments on related systems. The expected main features for the structure of water molecules solvating B‐DNA with Na+counterions are briefly discussed at the end of

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200309

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe helix–coil transition and conformational structure of poly(8‐bromoadenylic acid) [poly(8BrA)] have been investigated using1H‐ and13C‐nmr, CD, and ir spectroscopy. The results have been compared with the structure of the related 5′‐mono‐ and polynucleotides. The chemical shifts of H(2′), H(3′), C(2′), and C(3′) nmr signals show an interesting correlation with both the puckering of ribose ring and glycosidic bond torsion angle. Poly(8BrA) shows an upfield shift of the C(3′) signal and a downfield shift of the H(3′) signal compared to the chemical shifts in poly(A). These shifts are consistent with a C(3′)endo‐synconformation for poly(8BrA). A similar effect has been reported previously and is also observed here on the C(2′) and H(2′) signals when the preferred conformation is C(2′)endo‐syn(e.g., in 5′‐8BrAMP). The chemical‐shift parameters thus act as a probe for studyingsyn⇄antiand N ⇄ S equilibria in solutions. The three‐bond1H‐′13C coupling constants between H(1′) and C(8) and C(4) have been measured in poly(8BrA) and 5′‐8BrAMP and their structural implications have been discussed. The observed preference of a C(3′)endo‐synconformation for poly(8BrA), coupled with other evidence, throws doubt on the validity of a correlation previously reported whereby asynconformation is associated with a C(2′)endoribose pucker. The backbone conformation of randomly coiled poly(8BrA) is very similar to the structures found in polyribonucleotides: poly(A) and poly(U). All three polymers show strong preferences for the backbone angles found in RNA helices. The CD spectrum of poly(8BrA) has a striking relationship to that of poly(A). The signs of all extrema are inverted, and the magnitudes are related by a constant factor. We suggest that these differences result from a change in the angle between coupled transition moment vectors in the two polymers. Infrared spectra of poly(8BrA) in H2O and D2O solution are reported for the frequency range below 1400 cm−1. The antisymmetric>PO 2−stretching vibration is observed at an unusually low frequency in the helix (1214 cm−1). The symmetric>PO 2−stretch occurs at ∼1095 cm−1but is not resolved from a ring vibration near this frequency. A conformationally sensitive band, characteristic of helical RNA structures, is observed at 817 cm−1and disappears when the helix is melted. This observation confirms the conclusion that ordered poly(8BrA) has a regular helical structure with an RNA backbone conformation. A stereochemical explanation is provided for the failure of p

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200310

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe fractions obtained from the partially hydrolyzed branchedStreptococcus salivariuslevan were examined in solution. Sedimentation coefficients,S0, intrinsic viscosities, [η], weight‐average molecular weights,Mw, and radii of gyration were obtained from sedimentation velocity, viscosity, and light‐scattering measurements. Double logarithmic plots of [η] vsMwandS0vsMweach yielded two linear segments intersecting atMw≈ 105. Hydrodynamic data suggest that fractions ofMw>105behave as compact spheres, whereas forMw<105, the particles are best characterized as linear random coils. Calculations based on theories of random coils and spheres support the above obser

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200311

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

年代:1981

数据来源: WILEY