A potassium-39 NMR study of potassium binding to double-helical DNA.

The binding of K+ to double-helical DNA has been examined by 39K NMR. The results obtained are in substantial agreement with previous measurements of 23Na+ binding to DNA. Thus, in both cases the fractional neutralization of DNA phosphate charge appears independent of the total univalent cation concentration. Further, the dependences of the 23Na+ and 39K+ linewidths on Mg2+ and on temperature are strikingly similar. The implications of these results are discussed in terms of current theories of counterion binding to cylindrical polyelectrolytes.