SynopsisThe electrophoretic mobility of DNA in the presence of tetramethylammonium and alkali metal ion chlorides has been studied as a function of ionic strength. Each cation exhibits a characteristic behavior in accord with the idea that the order of interaction with DNA is Li+ > Na+ > K + > TMA+. The application of theories of the electrophoresis of polyelectrolytes is discussed, leading to an attempt to calculate the fractional charge per DNA phosphorus from the mobility data. Over the range 0.05-0.4M a constant and unique value of the DNA charge is obtained in the presence of each cation. Values of the zeta potential and of the friction factor per monomer unit are also ralrulated.

SynopsisThe effect of small quantities of metal ions on the electrophoretic mobility of calf thymus DNA in solutions maintained a t 0.2 ionic strength with weakly interacting (CHa)4N + ions yields information about interactions occurring in a region very close to the polymer chain. By means of this technique, it is demonstrated that the binding order to DNAis Li+> Na+> K+for thealkaIimetaIionsandMn++> Mg++> Ca++ for the divalent ions studied. The quantitative details are compared to earlier work on the long-chain polyphosphates. Close agreement between the two systems is obtained indicating that an intrinsic property of individual phosphate groups is being observed and that minor discrepancies probably arise from secondary factors. Three types of stability constants representing the binding of alkali metal ions to DNA are calculated and although differing in absolute magnitude, they all satisfactorily represent the result that the order of interaction is Li+ > Na+ > K + with respective relative strengths of 1.5: 1 : 0.8.

SynopsisIn order to examine the thermodynamic effects of exposing nucleic acid bases to water, we have measured the solubility of adenine, cytosine, and uracil in water and in organic solvents as a function of temperature. Transfer of a nucleic acid base from an organic environment into water is characterized by positive values for AH and for AS. We conclude from this result that the overall interaction between nucleic acid bases and water cannot be hydrophobic. If the effect we observe represents structure breaking in water by nucleic acid bases, this process would account for a major portion of the large, positive melting entropy of DNA, and would also con tribute substantially to the melting enthalpy.