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Biophys J, September 2001, p. 1580-1587, Vol. 81, No. 3
Department of Chemistry-Biology, University of Québec at Trois-Rivières, Québec G9A 5H7, Canada
Ag(I) is a strong nucleic acids binder and forms several
complexes with DNA such as types I, II, and III. However, the details of the binding mode of silver(I) in the Ag-polynucleotides remains unknown. Therefore, it was of interest to examine the binding of Ag(I)
with calf-thymus DNA and bakers yeast RNA in aqueous solutions at pH
7.1-6.6 with constant concentration of DNA or RNA and various
concentrations of Ag(I). Fourier transform infrared spectroscopy and
capillary electrophoresis were used to analyze the Ag(I) binding mode,
the binding constant, and the polynucleotides' structural changes in
the Ag-DNA and Ag-RNA complexes. The spectroscopic results showed that
in the type I complex formed with DNA, Ag(I) binds to guanine N7 at low
cation concentration (r = 1/80) and adenine N7 site
at higher concentrations (r = 1/20 to 1/10), but not to the backbone phosphate group. At r = 1/2,
type II complexes formed with DNA in which Ag(I) binds to the G-C and
A-T base pairs. On the other hand, Ag(I) binds to the guanine N7 atom
but not to the adenine and the backbone phosphate group in the Ag-RNA complexes. Although a minor alteration of the sugar-phosphate geometry
was observed, DNA remained in the B-family structure, whereas RNA
retained its A conformation. Scatchard analysis following capillary
electrophoresis showed two binding sites for the Ag-DNA complexes with
K1 = 8.3 × 104
M
1 for the guanine and K2 = 1.5 × 104 M
1 for the adenine bases.
On the other hand, Ag-RNA adducts showed one binding site with
K = 1.5 × 105 M
1
for the guanine bases.
Biophys J, September 2001, p. 1580-1587, Vol. 81, No. 3
© 2001 by the Biophysical Society 0006-3495/01/09/1580/08 $2.00
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