The model polynucleotide poly(dG-dC).poly(dG-dC) (polyGC) was titrated with a strongacid (HCl) in aqueous unbuffered solutions and in the quaternary w/o microemulsionCTAB/n-pentanol/n-hexane/water. The titrations, performed at several concentrations ofNaCl in the range 0.005 to 0.600 M, were followed by recording the modifications of theelectronic absorption and of the CD spectra (210≤ λ ≤350 nm) upon addition of the acid. Insolution, the polynucleotide undergoes two acid-induced transitions, neither of which correspondsto denaturation of the duplex to single coil. The first transition leads to theHoogsteen type synG.C+ duplex, while the second leads to the C+.C duplex. The initial Bformof polyGC was recovered by back-titration with NaOH. The apparent pKa values wereobtained for both steps of the titration, at all salt concentrations. Areasonably linear dependenceof pKa(1) and pKa(2) from p[NaCl] was obtained, with both pKa values decreasing withincreasing ionic strength.In microemulsion, at salt concentrations ≤ 0.300 M, an acid-induced transition wasobserved, matching the first conformational transition recorded also in solution. However,further addition of acid led to denaturation of the protonated duplex. Renaturation ofpolyGC was obtained by back-titration with NaOH.At salt concentrations > 0.300 M, polyGC is present as a mixture of B-form and ψ(-) aggregates,that slowly separate from the microemulsion. The acid titration induces at first a conformationaltransition similar to the one observed at low salt or in solution, then denaturationoccurs, which is however preceded by the appearance of a transient conformation, thathas been tentatively classified as a left-handed Z double helix.
|Numero di pagine||13|
|Rivista||JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS|
|Stato di pubblicazione||Published - 2006|
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology