[Mechanism of hydrogen exchange in DNA]

The hydrogen exchange mechanism of DNA bases imino- and amino protons is explained according to a suggested exchangeable state model. This state can be formed as a result of significant structural fluctuations which are not complete base pair openings. The exchangeable state model represents the hydrogen-bonded complex of two nucleotide bases and one water molecule made up dynamically. Quantum-mechanical calculations for the values of energy as the function of H-bond proton positions in the complex were carried out and the two-proton positions in the complex were carried out and the two-proton transfer is shown to be possible. The suggested model allows to give a noncontradictary interpretation of the hydrogen exchange data in double-helical polynucleotides.