A kinetic study of 1H leads to 3H exchange in C(8) H-groups of purinic residues in DNA.

The kinetic study of 1H leads to 3H exchange in C(8) H-groups of purinic residues of DNAs with different G-C content as well as in corresponding dNMP mixtures have been carried out. The present results show that 1H--3H exchange in DNA is retarded (as compared to the exchange in dNMP mixtures) to a lesser extent (Kret =2.4-2.8) than in RNA (Kret=6-8). The degree of retardation in these polymers is practically independent of their nucleotide composition. Assuming the ylide mechanism of exchange reaction it is suggested that the lower rate of 1H leads to 3H exchange in C(8) H-groups of purinic residues in polynucleotides of A-form (RNA and other polyribonucleotides) as compared to those of B-form (DNA and other polydeoxyribonucleotides) might be accounted for by decreased availability of C(8) H-groups for OH-ions of the solvent due to a different microenviroment of these groups in A- and B-type helixes.