INFLUENCE OF POLYELECTROLYTE PROPERTIES OF DNA ON CYTOSINE PROTONATION

The polyelectrolyte properties of DNA affect cytosine protonation. The existence of a local region of lower pH in close proximity to the DNA chain is supposed to explain this phenomenon. Such a region was revea led by absorption spectroscopy with the use of Methyl Red (C15H15N3O2) . Differences in the protonation of cytosines in different polyelectro lyte environments were detected spectrophotometrically under identical ionic and other conditions. The polyelectrolyte properties of DNA wer e proved to determine cytosine protonation at physiological pH. The di fferences in the protonation of cytosines were also observed in the st udies of double-stranded high- and low-molecular DNA of the same nucle otide composition at low ionic strengths. The protonation of cytosine is shifted to the lower pH region for the high-molecular DNA as compar ed with fragments of lower molecular weight.