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Interactions of calf-thymus histone fractions in aqueous solution with 8-anilinonaphthalene-1-sulphonic acid.

ABSTRACT: 1. The interactions of histone fractions with 8-anilinonaphthalene-1-sulphonic acid were investigated by fluorimetry and spectrofluorimetry and the results were interpreted with the aid of equilibrium-dialysis techniques. 2. Characteristic differences were found between the various histone fractions, and with fractions F3 and F2a the binding was found to be salt-dependent. 3. Evidence was obtained indicating a slow change of the physical state of fractions F3 and F2a in the presence of salt, and the binding by these two fractions in the presence of salt was greater by an order of magnitude than by fractions F1 and F2b. 4. Conditions favouring binding were also those favouring histone aggregation; SO(4) (2-) ions activated binding at a lower concentration than Cl(-) ions; urea, guanidinium ions and high concentrations of I(-) ions were inhibitory to binding. 5. After histones had been kept in the presence of salt for a long time the reversal of interaction on decreasing the salt concentration was incomplete. 6. The inhibition of binding by fraction F2a in the presence of urea or fraction F2b depended on the time sequence of addition of the reagents. 7. Artificial nucleoproteins made by precipitating DNA with the histone fractions in neutral 0.14m-sodium chloride showed the same order of interaction as was found for the fractions in solution. 8. Comparison of the binding by fraction F2a with that by bovine plasma albumin showed that in both cases there were a large number of weakly binding sites but that fraction F2a lacked the small number of strongly binding sites found in albumin. No slow change of binding in the presence of salt was found for albumin. 9. Binding by fraction F2b increased the affinity of the protein for further molecules of the adsorbate. 10. The results are discussed in relation to the close relationship between binding and aggregation and the possible role of non-polar interactions as determined by the balance between polar and non-polar amino acids in the histone fractions.

SUBMITTER: Laurence DJ

PROVIDER: S-EPMC1265011 | biostudies-other | 1966 May

REPOSITORIES: biostudies-other

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Project description:Previous investigations were conducted on two concentrations of DNA solution: 4 mg/mL, for which it has been shown that no supramolecular organization is induced under flow at low shear rates; and 10 mg/mL, in which a liquid crystalline-type texture is formed under flow at low shear rates, attesting to an orientation of pre-organized chains. Rheological experiments are discussed and their results supported by small-angle X-ray scattering (SAXS) and flow birefringence visualization experiments. Scattering from polyelectrolytes has a characteristic signal, which is here observed in SAXS, showing a strong correlation peak between charged chains in water, for both concentrations. This peak is weaker in the presence of 0.01 M NaCl and suppressed in salt excess at 0.1 M NaCl. No plateau in the ?( ? ? ) plot was observed in analysis of rheological experiments on low DNA concentration (4 mg/mL). As typically observed in polyelectrolyte systems both the dynamic moduli and shear viscosity were higher in water as electrostatic forces dominate, than in the presence of salt, especially at low shear rates. The rheological results for concentrations of 0.01 M NaCl are lower than in water as expected due to partial screening of electrostatic repulsions. Rheological data for concentrations of 0.1 M NaCl are unexpected. Electrostatic forces are partially screened in the low salt concentration, leading to a drop in the rheological values. For high salt concentration there are no longer interchain repulsions and so steric interactions dominate within the entangled network leading to the subsequent increase in rheological parameters. Regardless of the solvent, at high shear rates the solutions are birefringent. In the 10 mg/mL case, under flow, textures are formed at relatively low shear rate before all the chains align going to a pseudonematic liquid crystalline phase at high shear rate. The electrostatic repulsion between semi-rigid chains induces a correlation between the chains leading to an electrostatic pseudo-gel in water and loosely in 0.01 M NaCl at low stress applied. To the best of our knowledge, this is the first time that such behavior is observed. In 0.1 M NaCl, DNA behavior resembles the corresponding neutral polymer as expected for polyelectrolyte in salt excess, exhibiting a yield stress. When texture appears in water and in 0.01 M NaCl, a critical transition is observed in rheological curves, where the viscosity decreases sharply at a given critical shear stress corresponding to a plateau in the ?( ? ? ) plot also observed in creep transient experiment.

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Interactions of calf-thymus histone fractions in aqueous solution with 8-anilinonaphthalene-1-sulphonic acid.

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