摘要：

The interaction of a high molecular weight sample of calf thymus desoxyribonucleic acid (UNA) with the fluorescent cationic dye acriflavine was studied in the concentration range where soluble complexes are formed and was found to be reversible. Determinations of the amount of binding were made over a wide range of equilibrium concentrations of unbound acriflavine, at several values of the experimental variables ionic strength, pH and temperature, by means of the partition analysis method. It was found that the binding sites for acriflavine on the DNA molecule are heterogeneous with respect to their intrinsic association constants and that the binding curves may be described in terms of a two-constant equation. The maximum number of sites available for complexing with acriflavine per DNA phosphate group is approximately 0.5 at ionic strength 0.002 at pH. 7. A method for the treatment of fluorescence quenching data was developed which takes into account the multiple equilibria involved in macrpmolecular interactions. This method yields values for k1, the equilibrium constant for the first DNA-acriflavine association, in agreement with the independent partition analysis results. As is expected for an electrostatic interaction, k1 decreases with increasing ionic strength and with decreasing pH, but the evidence indicates that secondary binding forces are important. The enthalpy changes are rather large and negative. The corresponding standard entropy changes are zero within experimental error, suggesting that the macromolecular configuration of DNA does not change significantly upon interaction with acriflavine.

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