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1.
The thermal stability and renaturation kinetics of DNA have been studied as a function of dimethyl sulfoxide (DMSO) concentration. Increasing the concentration of DMSO lowers the melting temperature of DNA but results in an increased second-order renaturation rate. For example, in a DNA solution containing 0.20M NaCl, 0.01M Tris (pH 8.0), and 0.001M EDTA, the addition of 40% DMSO lowers the melting temperature of the DNA by 27°C and approximately doubles the optimal renaturation rate. The effect of DMSO on the renaturation rate is shown to be at least partially due to its effect on the solution dielectric constant and to be consistent with the polyelectrolyte counterion condensation theory of Manning [(1976) Biopolymers 15 , 1333–1343]. 相似文献
2.
Various molecular parameters, which characterize sodium hyaluronate in 0.2M NaCl solution, were obtained at 25°C by means of the static and dynamic light scattering and low shear viscometry over the molecular weight range of 5.94–627 × 104. Molecular weight distribution was obtained by using the Laplace inversion method of the autocorrelation function of the scattered light intensity and by Yamakawa theory for the wormlike chain with the stiff chain parameters for sodium hyaluronate in 0.2M NaCl (persistence length, chain diameter, molar mass per unit contour length, and the excluded‐volume strength). The molecular weight distribution thus obtained reproduced the solution properties of sodium hyaluronate well. Especially, the intrinsic viscosity showed a good agreement over four orders of molecular weight with Yamakawa theory combined with the Barrett function. Sodium hyaluronate in 0.2M NaCl solution is well expressed by the wormlike chain model affected by the excluded‐volume effect with the persistence length of 4.2 nm. © 1999 John Wiley & Sons, Inc. Biopoly 50: 87–98, 1999 相似文献
3.
Six samples of Na xanthan in 0.01M aqueous NaCl containing 0.01 N HCl (pH = 2) were studied by light scattering and viscosity. This study was motivated by the finding that the intrinsic viscosity [η] fairly sharply decreased when the pH of the solvent was lowered from about 6 to 2 by adding HCl to 0.01M aqueous NaCl in which Na xanthan dissolves as rigid dimers having a double-helical structure. The data for weight-average molecular weight, radius of gyration, and [η] showed that Na xanthan at pH = 2 remains a dimer behaving as a semiflexible chain. Data analysis in terms of known theories for unperturbed wormlike chains yielded 0.47 ± 0.02, 2.0 ± 0.6, and 68 ± 7 nm for the contour length h per main-chain residue, diameter d, and persistence length q of the dimer, respectively. these h and d values agreed with the pitch per main-chain residue and the diameter of the double helix of Na xanthan in 0.01 or 0.1M aqueous NaCl. However, the q value, which was close to the intrinsic persistence length q0 ( = q in the absence of electrostatic interaction) of Na xanthan at pH = 2, was much smaller than the q0 (106 nm) of this helix. We concluded that the xanthan dimer at pH = 2 assumes a double-helical structure, which is geometrically the same as, but is more flexible than, that at neutral pH. 相似文献
4.
Rodney E. Harrington 《Biopolymers》1978,17(4):919-936
Excluded volume and persistence length of high-molecular-weight DNA from T2 bacteriophage have been evaluated over a range of NaCl concentrations from 0.005 to 2.0M using low-shear flow-birefringence and intrinsic-viscosity data. Uncertainty in persistence length due to ambiguity in the assignment of intrinsic birefringence has been avoided by calibrating the data at 0.2M NaCl using a recently reported persistence-length value based upon photon correlation spectroscopy [Jolly, D. & Eisenberg, H. (1976) Biopolymers 15 , 61]. Results at high salt concertrations are in satisfactory agreement with other estimates of excluded volume and chain flexibility in the literature, but at very low salt concentrations they reflect greater chain expansion than has heretofore been reported. The extinction-angle data imply a transition from a nondraining chain with excluded volume at 0.1M NaCl to an almost freely draining chain at 0.005M NaCl. Over this same salt range, the experimental persistencelength data agree very well with Flory's thermodynamic chain-expansion theory [Flory, P. J. (1953) J. Chem. Phys. 21 , 162], but are in generally poor agreement with other theoretical treatments. A detailed comparison of the results with other data in the literature suggests that the combined flow-birefringence-intrinsic-viscosity technique employed here may be more sensitive to the distribution of chain stiffness and excluded volume in polyelectroytechain expansion of DNA than are othe rhydrodynamic methods such as sedimentation or intrinsic viscosity alone. 相似文献
5.
Magnetic birefringence study of the electrostatic and intrinsic persistence length of DNA 总被引:1,自引:0,他引:1
Magnetic birefringence experiments were performed on solutions of DNA of intermediate molecular weight at several concentrations (cp) over a wide range of ionic strengths (of NaCl and MgCl2). The specific Cotton-Mouton constant (CM/cp) is found to be independent of cp when contributions from cp to the ionic strength (μeff) are taken into account according to the concept of counterion condensation. For μeff ? 10?2M, CM/cp is also independent of the ionic strength; the plateau value results in an acceptable value of the intrinsic persistence length, when a revised theoretical expression for the magnetic birefringence of wormlike chains is used, combined with new experimental data for the monomeric optical and magnetic anisotropy. For μeff < 10?2M, CM/cp strongly, or wealky, increases with decreasing μeff, depending on the valency of the counterion used (Na+ or Mg2+, respectively). This increase agrees quantitatively with the variation of the electrostatic persistence length as predicted by Odijk [(1977) J. Polym. Sci. Polym. Phys. Ed. 15 , 477–483], Odijk and Houwaart [(1978) J. Polym. Sci. Polym. Phys. Ed. 16 , 627–639], and by Skolnick and Fixman [(1977) Macromolecules 10 , 944–948]. A comparison with other experimental data seems to reveal the importance of excluded-volume effects, which are particularly pronounced in the low-salt regime. 相似文献
6.
Thermodynamics of the daunomycin-DNA interaction: ionic strength dependence of the enthalpy and entropy 总被引:2,自引:0,他引:2
J B Chaires 《Biopolymers》1985,24(2):403-419
Fluorescence and absorbance methods were used to study the interaction of daunomycin with calf-thymus DNA over a wide range of temperatures and NaCl concentrations. van't Hoff analysis provided estimates for the enthalpy of the binding reaction over the NaCl range of 0.05–1.0 M. Daunomycin binding is exothermic over this entire range, and the favorable binding free energy arises primarily from the large, negative enthalpy. Both the enthalpy change and entropy change are strong functions of ionic strength. Possible molecular contributions to the enthalpy and entropy are discussed, leading to the tentative conclusion that hydrogen-bonding interactions at the interacalation site are the primary contributors to the observed thermodynamic parameters. The dependence of the enthalpy on the ionic strength is well beyond the predictions of current polyelectrolyte theory and cannot be fully accounted for. The enthalpy and entropy changes observed compensate one another to produce relatively small free-energy changes over the range of solution conditions studied. 相似文献
7.
Takahide Saito Naomichi Iso Haruo Mizuno Nobuhiko Onda Hideyuki Yamato Hiroshi Odashima 《Biopolymers》1982,21(4):715-728
The persistence length of lugworm cuticle collagen in 0.1M acetic acid was evaluated as 1600 ~ 1800 Å by Yamakawa-Fujii's model for a wormlike chain from the sedimentation constant and the intrinsic viscosity. The persistence length was further examined for a series of sample “collagen sonicates” produced by varying the duration of sonic irradiation. To estimate the salt effect on the persistence length, measurements were made over a range of NaCl concentrations from 0 to 0.1M. The results showed that the cuticle collagen and collagen sonicates had identical values of persistence length and that the neutral salt effect for the cuticle collagen was far smaller than that for DNA. 相似文献
8.
At low salt ([Na+] = 10?3M), spermidine is capable of transforming DNA from a highly extended random coil to a compact particle. The transition takes place at a spermidine concentration of around 25 μM and the compact particle has been previously studied in considerable detail for several different DNAs. The objective of the present study is to see what effect, if any, spermidine has on T7 DNA conformation prior to collapse using flow dichroism and intrinsic viscosity. We conclude that increasing the spermidine concentration from 0 to the collapse transition point (above 20 μM) makes DNA increasingly nondraining. Furthermore, the persistence length dropped from 785 (±42) to 560 (±32) to 445 (±26) Å on increasing the ambient spermidine concentration from 0 to 1 to 10 μM. These results are in good agreement with counterion condensation theory and Odijk's theory of the electrostatic contribution to the persistence length of DNA. Nonetheless, it is concluded that counterion condensation is not entirely responsible for DNA collapse and that crosslinking promotes the transition to the compact state. 相似文献
9.
The secondary structure of xanthan in solutions of relatively low salt concentration and at room temperature has been investigated using static light scattering experiments. Additional evidence has been found for a dimeric structure at 25°C in 0.01M NaCl. From the experimental z-average mean square (ms) radius of gyration, a value for the persistence length p has been estimated, taking explicitly into account the polydispersity of the three samples used, which has been established by gel permeation chromatography (GPC) measurements. The experimental particle scattering functions of the three samples are consistent with theoretical estimates for polydisperse systems with the same value of p = 65 ± 10 nm and the molar mass per unit length for a dimeric structure. This secondary structure remains unaffected by the ionic strength in the 0.005–0.0lM range. Partial aggregation seems to occur at higher NaCl concentrations. Light scattering and GPC data show that heating the xanthan 0.01M NaCl solutions to about 70°C considerably reduces the Mw of the low molar mass sample (2.3 × 105-g·mol?1), contrary to what is observed for the high molar mass sample (1.8 × 106-g·mol?1). These experimental findings can be accounted for by a partial temperature-induced dissociation of the xanthan dimers according to an all-or-none mechanism. © 1994 John Wiley & Sons, Inc. 相似文献
10.
J. D. Wells 《Biopolymers》1973,12(2):223-227
The range of application of the Manning theory of polyelectrolyte solutions (J. Chem. Phys., 51 , 924 (1969)) is extended to finite concentrations of simple electrolyte by the empirical superposition of excess free energies arising from (i) interactions between mobile ions and polyions and (ii) mutual interactions between mobile ions. A comparison of published results with the modified theory shows excellent agreement over a wide range of concentrations. Results for a polyelectrolyte of low charge density suggest that the effective inter-charge spacing may be less than that of the fully extended polyion. 相似文献
11.
Summary The effects of increasing concentrations of NaCl and CaCl2 on quince (Cydonia oblonga Mill. BA 29 clone) somatic embryogenesis and adventitious root regeneration were investigated. Leaves collected from in vitro-grown shoots were used as explants and induced for 2d in liquid Murashige and Skoog medium containing 11.3 μM 2,4-dichlorophenoxyacetic acid. Explants were then cultured on semisolid Murashige and Skoog medium enriched with 4.7 μM kinetin and 0.5 μM naphthaleneacetic acid under red light for 25 d and under white light for another 25 d. Two experiments were performed: in
the first, NaCl was used at 0,25, 50, 100, and 200 mM in factorial combination with CaCl2 at 3, 9, and 27 mM; in the second, NaCl was applied at 0, 5, 10, 20, 40, and 80 mM in combination with CaCl2 at 0.3, 1.0, and 3.0 mM. Quince leaves revealed the capacity to regenerate somatic embryos and/or adventitious roots. Quantitative and qualitative
regeneration from leaves was affected by NaCl treatments: increasing NaCl concentrations, in combination with CaCl2 at 1 mM, led to an increase in the proportion of leaves producing somatic embryos only, and to a decrease of both leaves regenerating
roots only and leaves simultaneously producing somatic embryos and adventitious roots. This suggests a beneficial effect of
salt stress on the embryogenic process. The regeneration response decreased with increasing salt concentrations and was almost
totally inhibited above 50 mM NaCl and 9 mM CaCl2. The presence of CaCl2 in the culture medium apparently mitigated the effects of salt stress, but only when NaCl was applied at 40 mM. NaCl at 5 mM, in the presence of 0.3 or 1 mM CaCl2, was favorable both to somatic embryo and root production. No value of the ratio Na+/Ca2+ was found to be optimal for the regeneration processes. 相似文献
12.
Pavlov G Finet S Tatarenko K Korneeva E Ebel C 《European biophysics journal : EBJ》2003,32(5):437-449
The hydrodynamic characteristics of heparin fractions in a 0.2 M NaCl solution have been determined. Experimental values varied over the following ranges: the sedimentation coefficient (at 20.0 °C), 1.3<s0×1013<3.2 s; the Gralen coefficient (sedimentation concentration-dependence parameter), 10<ks<70 cm3 g–1; the translational diffusion coefficient, 3.9<D0×107<15.4 cm2 s–1; the intrinsic viscosity, 7.9<[]<40 cm3 g–1. Combination of
s0 with D0 using the Svedberg equation yielded molecular weights in the range 3.9<M×10–3<37 g mol–1. The value of the mass per unit length of the heparin molecule,
ML, was determined using the theory of hydrodynamic properties of a weakly bending rod, giving
ML=570±50 g nm–1 mol–1. The equilibrium rigidity, Kuhn segment length (A=9±2 nm) and hydrodynamic diameter (d=0.9±0.1 nm) of heparin were evaluated on the basis of the worm-like coil theory without the excluded volume effect, using the combination of hydrodynamic data obtained from fractions of different sizes. Small-angle X-ray scattering for three heparin fractions allowed an estimate for the cross-sectional radius of gyration as 0.43 nm; from the evolution with the macromolecule contour length of the radius of gyration, a value for the Kuhn segment length of 9±1 nm was obtained. A good correlation is thus observed for the conformational parameters of heparin from hydrodynamic and X-ray scattering data. These values describe heparin as a semi-rigid polymer, with an equilibrium rigidity that is essentially determined by a structural component, the electrostatic contribution being negligible in 0.2 M NaCl.Presented at the conference for Advances in Analytical Ultracentrifugation and Hydrodynamics, 8–11 June 2002, Grenoble, France 相似文献
13.
FRANZ-ARNOLD AUSTENFELD 《Physiologia plantarum》1976,36(1):82-87
The response of glycolate oxidase from shoots of Salicornia europaea L. and from leaves of Pisum sativum L. to salt treatment during assay was studied by DCPIP reduction and O2 uptake. In Pisum there was found up to five times more glycolate oxidase activity per gram fresh weight than in Salicornia. However, the calculation of the specific activity pointed out that this result was caused only by the high level of enzyme protein in Pisum, and that specific activity from both species was of equal size. By the DCPIP method it was shown that in test media containing up to 1.0 M NaCl or KCl glycolate oxidase of Salicornia was of equal size compared with the control (medium without additional salts). With 2.0 M NaCl or KCl the activity decreased by about 80 and 30% respectively. Glycolate oxidase of Pisum was somewhat more salt sensitive. 1.0 M NaCl or KCl reduced the activity by about 35%. In the presence of 2.0 M NaCl or KCl the enzyme activity from Pisum was inhibited to about 80 and 60% respectively. By substituting sulfates for chlorides the activity of glycolate oxidase from both Salicornia and Pisum was stimulated strongly. 1.5 M Na2SO4 and 0.5 M K2SO4 (both are saturated solutions) caused an increase of glycolate activity from Salicornia of about 225 and 185% respectively, and from Pisum of about 50 and 30% respectively. Studying the response of glycolate oxidase to salt treatment by O2 uptake one must establish that with this method the degree of inhibition of enzyme activity at higher salt concentrations was always more severe than with dye reduction. Addition of 1.0 M NaCl or KCl to the assay medium caused an inhibition of glycolate oxidase activity from Salicornia of about 50% and from Pisum of about 60%. 2.0 M NaCl or KCl reduced the enzyme activity of both Salicornia and Pisum to nearly 10% of control activity. Furthermore, in contrast to DCPIP reduction no stimulating effect of sulfates on glycolate oxidase activity was detectable. Indeed, the inhibitory effect of sulfates was very slight. 1.0 M Na2SO4 caused a mean inhibition of glycolate oxidase activity of only 15% with both species, and in the presence of 1.5 M Na2SO4 50% of control activity was measured. At maximal K2SO4 concentrations (0.5 M) glycolate oxidase from both Salicornia and Pisum was also unaffected. It is supposed that the described salt tolerance of glycolate oxidase in vitro, possibly is due to an adaptation of the enzyme to high salt levels within peroxisomes in vivo. 相似文献
14.
Extinction angles, flow birefringence, and intrinsic viscosities are compared for linear, bihelical DNAs from viral and other sources that span a range in molecular weight from ~105 to 1.3 × 108. This range effectively spans the region over which transition from rigid-rod to expanded-coil hydrodynamic property behavior occurs. All DNAs are in identical, phosphate–EDTA, neutral-pH buffers, 0.1M in NaCl. The extinction angle is a hydrodynamic property only and is thus particularly sensitive to effects of kinetic chain rigidity or internal viscosity. Our extinction angle results cannot be interpreted by any simple, single-function theoretical expression. Rather, they must be divided into distinct high- and low-molecular-weight domains. The low-molecular-weight region is typical of rigid-particle opticohydrodynamic property behaviour characterized primarily by particle orientation. The high-molecular-weight domain shows evidence for a finite internal viscosity effect, however, which can be interpreted as very nearly Kuhnian using Cerf's amplification of the Gaussian subchain model to include internal viscosity. It is found that the high-molecular-weight, monodisperse viral DNAs from T7, T5, and T2 bacteriophage show an internal viscosity contribution to the limiting extinction angle–shear rate ratio of ~3 × 10?3 s. An effect of this magnitude may be marginally important in interpreting extinction angle and certain other hydrodynamic property data for high-molecular-weight DNA systems. Internal viscosity effects do not appear to be manifest in the ratio of flow birefringence to intrinsic viscosity, however, and the persistence length of the high-molecular-weight DNAs is found to be independent of molecular weight to within estimated experimental uncertainty. 相似文献
15.
We report the first study of the effect of NaCl on the double-bond isomeric composition of fatty acids and theirsn-1/sn-2 positional distribution in the membrane phospholipids of a moderately halophilic eubacterium. The major phospholipids, phosphatidylethanolamine and phosphatidylglycerol, ofVibrio costicola grown in 1M or 3M NaCl both have ansn-1 saturated,sn-2 unsaturated distribution of fatty acids. There is a greater effect of salinity on the fatty acid composition of phosphatidylglycerol compared with phosphatidylethanolamine. The fatty acids in phosphatidylethanolamine of cultures grown in 1M compared with 3M NaCl have the same unsaturation index and average chain length, but different double-bond isomeric compositions. In comparison, the fatty acid composition of phosphatidylglycerol is more unsaturated, with a different double-bond isomeric distribution, and has a shorter average chain length in cultures grown in 3M compared with 1M NaCl. The pattern of fatty acid isomers of 16:1 and 18:1 shows thatV. costicola uses the anaerobic pathway of fatty acid biosynthesis. The presence of the isomers 16:1c11 and 18:1c13 in the phospholipids of cultures grown in 3M but not in 1M NaCl indicates that external salinity affects the specificity of fatty acid synthetase in this moderately halophilic bacterium. 相似文献
16.
Summary Growth sensitivity of four local grapevine (Vitis vinifera) varieties, Ashlamesh, Helwani, Kassofee, and Khoudeiry, were evaluated for salt. They were cultured on DSD1 medium until
rooting stage, then they were transferred to a liquid DSD1 medium containing 0, 10, 20, 30, 40, 80, 120, or 150 mM NaCl for 30 d. The shoot length and leaf number of Ashlamesh, Helwani, and Kassofee were significantly increased at 10 and/or
30 mM NaCl, whereas, 150 mM NaCl decreased shoot length of all varieties except Kassofee. The presence of NaCl at 80 mM or higher concentrations decreased the chlorophyll content and root number of all varieties, while 30 mM NaCl increased root number of Kassofec. 相似文献
17.
Complexes of DNA with histone H1 and random and sequential polypeptides containing 30–100% of lysine were studied using actinomycin D as a probe. The binding of actinomycin D was measured by spectrophotometric titration in 0.15M NaCl and in 0.01M Tris buffer. The excluded-site model was used for the evaluation of binding data. Polypeptides reduce the number of binding sites on DNA available for actinomycin D binding. The extent of this change depends mainly on the content and distribution of basic lysine residues. Of the hydrophobic residues constituting the peptides, only leucine strongly depresses the actinomycin D binding. The helix-forming and helix-breaking amino acid residues are without effect. 相似文献
18.
Robert L. Cleland 《Biopolymers》1984,23(4):647-666
Fractionated samples of sodium hyaluronate of low molecular weight were used to calibrate the carbazole method for glucuronyl analsis and to determine the density increment (based on dry weight) of 0.444 (±0.003) mL/g in water and 0.386 (±0.003) mL/g for samples dialyzed against 0.2M NaCl. Weight-average molecular weights obtained by high-speed sedimentation equilibrium were used to calibrate the limiting viscosity number [η] in 0.2M NaCl, which gave [η]/Mw = 0.0028 (±0.0002) mL/g, valid to Mw = 0.0028 (±0.0002) mL/g, valid to Mw = 105. Experimental data from this work and the literature, including viscosity and light- and small-angle x-ray scattering measurements, were compared to theoretical chain models of the Kratky-Porod (KP) wormlike and the helical wormlike (HW) chain, as treated by Yamakawa and collaborators. Although either model could be fitted to experimental data about equally well with consistent parameters, provided those for the HW chain were of weakly helical nature, calculation of the unperturbed meansquare end-to-end distance as a function of chain length from a conformational model favored the KP chain alternative. The parameters that provide the best fit to experimental data for the KP wormlike model are a persistence length of 4.5–5 nm and a diameter of 1.1 nm. The latter is resonable for a hydrated hydrodynamic cylinder in view of the approximate unhydrated value of 0.7 nm estimated from the density increment. 相似文献
19.
The effects of varying CaSO4 and NaCl levels on the nutrient content ofLeucaena leucocephala were established by examining the concentrations of Na, Ca, Cl, K and Mg in leucaena roots, stems and leaves. Leucaena was
grown in nutrient solution at four levels of CaSO4 (0.5, 1.0, 2.5 and 5.0 mM) and NaCl (1, 25, 50 and 100 mM), in randomized blocks with five replications. Leucaena excluded sodium from stems and leaves when NaCl concentration was
50 mM or less. Sodium uptake decreased as CaSO4 concentration increased. Calcium uptake was affected by NaCl concentration when substrate CaSO4 concentration was 0.5 mM. At this level, 100 mM NaCl caused a marked decrease in leaf calcium and a marked increase in leaf Cl. In all other treatments, Cl uptake was not
affected by CaSO4 concentration. Potassium uptake was strongly depressed as NaCl concentration increased at low Ca concentration, but this
effect was offset at high Ca. Magnesium uptake decreased as CaSO4 levels increased. 相似文献
20.
R. M. Mohammad M. Akhavan-Kharazian W. F. Campbell M. D. Rumbaugh 《Plant and Soil》1991,134(2):271-276
The first set of experiments identified sodium chloride (NaCl) tolerance of 92 accessions of Rhizobium meliloti L. from various rhizobia collections and arid and saline areas of the Intermountain West. Accessions were incubated in salinized (0, 176, 352, 528, 616, 704 or 792 m M) yeast extract mannitol (YEM) medium. Growth was measured by turbidity at 420 nm after 3 d in culture. Rhizobial strains were classified by their growth response at an optical density (OD) of 704 m M; Groups One and Two did not exceed 0.10 and 0.33, respectively. Forty three different rhizobial strains were identified as salt-sensitive and 49 as salt-tolerant at 704 m M NaCl. None grew in a saline solution of 792 m M NaCl.The second set of experiments investigated the drought tolerance of R. meliloti accessions that exhibited differential salt tolerance. Fifteen salt-sensitive and 15 salt-tolerant strains of R. meliloti from the first experiment were exposed to simulated drought stress by adding polyethylene glycol 6,000 (PEG-6,000) to the YEM medium at concentrations of 0, –0.4, –0.8 or –1.0 MPa. Rhizobium strains were incubated for 10 days at 25°C and growth turbidity was measured at 420nm. Growth turbidity of the 30 accessions ranged from 100% at –0.4 MPa to 0% at –1.0 MPa. With one exception, strains that were more drought-tolerant (at –1.0 MPa) were also more salt-tolerant (616 m M). However, some of the more salt-tolerant strains at 616 m M were not the more drought-tolerant stains at –1.0 MPa. These salt-and drought-tolerant Rhizobium accessions are excellent models to study the mechanism(s) of such resistance, and to elucidate the role of genetics of NaCl and drought tolerance. 相似文献