DNA–divalent metal cation interactions measured by electrophoretic light scattering

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Abstract
We have used the laser Doppler technique of electrophoretic light scattering to study the electrokinetic and gross conformational manifestations of the binding of divalent cations to DNA in low‐salt solutions. By electrokinetic assay, divalent ion affinities to DNA in the 5–500 μM range increase in the order Mn+2+2+2+2. The ELS spectra show that Cu+2 denatures double‐stranded DNA in the 50–200 μM concentration range, thereby augmenting the reduction in electrophoretic mobility. Counterion condensation theory correctly predicts the form of the electrophoretic mobility reduction for territorially bound ions such as Mg+2, but the absolute magnitudes of electrophoretic mobility predicted by an equation deduced from condensation theory overestimate our experimental values.