Theory of the delocalized binding of Mg(II) to DNA: preliminary analysis for low binding levels.

A simple theoretical equation for the binding of Mg2+ to DNA in the presence of excess 1:1 salt is derived from a model that does not specify discrete binding sites but rather allows the associated metal ions to move freely near the surface of the DNA polyion. Use of a numerical value for the free volume, determined uniquely, in a separate communication, by a free energy minimization, leads to predicted values for the Mg2+ binding constant that are in essential agreement with measured values taken from the literature.