DNA protonation at low ionic strength of solution

Abstract

Abstract UV differential spectroscopy and thermal denaturation were applied to investigate the protonation of native (6 °C) and denatured (70 °C) DNA at 10 −3 M of Na + in the range of pH 7,0 to 3,85. A decrease in the pH was found to deteriorate the thermal stability of DNA and to narrow the range of the helix‐coil transition due to preferential destabilization of G + C pairs. The pH dependence of the degree of helicity for native DNA is non‐monotonic and agrees with the protonation model proposed by Courtois et al. The proton binding to the bases is anticooperative for native DNA and noncooperative for denatured DNA. The ionization of the bases is characterized by p K′ = 4,7 for helical and by p K′ = 5,2 for coil DNA.