Single-stranded model oligodeoxyribonucleotides, each containing a single protonatable base-cytosine, adenine, guanine, or 5-methylcytosine-centrally located in a background of non-protonatable thymine residues, were acid-titrated in aqueous solution, with UV monitoring. The basicity of the central base was shown to depend on the type of the central base and its nearest neighbours and to rise with increasing oligonucleotide length and decreasing ionic strength of the solution. More complex model oligonucleotides, each containing a centrally located 5-methylcytosine base, were comparatively evaluated in single-stranded and double-stranded form, by UV spectroscopy and high-field NMR. The N3 protonation of the 5-methylcytosine moiety in the double-stranded case occurred at much lower pH, at which the duplex was already experiencing general dissociation, than in the single-stranded case. The central guanine:5-methylcytosine base pair remained intact up to this point, possibly due to an unusual alternative protonation on O2 of the 5-methylcytosine moiety, already taking place at neutral or weakly basic pH, as indicated by UV spectroscopy, thus suggesting that 5-methylcytosine sites in double-stranded DNA might be protonated to a significant extent under physiological conditions.
- Klíčová slova
- DNA methylation, methylcytosine, nucleobases, oligonucleotides, protonation,
- MeSH
- 5-methylcytosin metabolismus MeSH
- adenin metabolismus MeSH
- guanin metabolismus MeSH
- jednovláknová DNA * chemie metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- konformace nukleové kyseliny MeSH
- oligodeoxyribonukleotidy * chemie metabolismus MeSH
- osmolární koncentrace MeSH
- protony MeSH
- sekvence nukleotidů MeSH
- thymin metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
- Názvy látek
- 5-methylcytosin MeSH
- adenin MeSH
- guanin MeSH
- jednovláknová DNA * MeSH
- oligodeoxyribonukleotidy * MeSH
- protony MeSH
- thymin MeSH
