ABSTRACT
Differential UV spectra of DNA and its monomers that were induced by Ag+ ions were measured, and the effect of ions on the parameters of the helix-coil transition was studied. The data obtained confirm the existence of "strong" and "weak" modes of binding of Ag+ to DNA. The earlier proposed proton transfer from N1G to N3C, which is determined by the interaction of Ag+ with N7G (a "strong" complex), follows immediately from the shape of the differential UV spectra. The positive cooperativity of the binding of Ag+ to DNA upon the formation of a "weak" complex is due to the cooperativity of the transition of DNA to a new double-helical conformation. A model of this conformation is proposed which suggests the formation of Hougsteen GC and AT pairs.
Subject(s)
DNA/chemistry , Silver/chemistry , Cations, Monovalent , Spectrophotometry, UltravioletABSTRACT
The interaction of Ag+ ions with ribonucleotides of canonical bases in aqueous solution was studied by differential UV spectroscopy. Atoms coordinating silver ions (N7, O6 of guanosine 5'-monophosphate, N3, O2 of cytidine 5'-monophosphate, N7, N1, N3 of adenosine 5'-monophosphate and N3 of uridine 5'-monophosphate) and the binding constants characterizing the formation of appropriate complexes were determined. The differences in the relative affinity of Ag+ ions for the atoms of nucleotide bases correlate with the potential on them.
Subject(s)
Ribonucleotides/chemistry , Silver/chemistry , Adenosine Monophosphate/chemistry , Cytidine Monophosphate/chemistry , Guanosine Monophosphate/chemistry , Spectrophotometry, Ultraviolet , Uridine Monophosphate/chemistryABSTRACT
Experimental data on DNA melting in the presence of magnesium and calcium ions are compared with the calculated results by the "ligand" theory and "condensation" theory developed by de Marky and Manning (TMM). The maximum is observed in TMM dependences of DNA melting temperature change (delta Tm) on the ion concentration (D), absent in the experimental dependences and the "ligand" theory. The main cause of the discrepancy of calculated and experimental dependences delta Tm (D) is the fact that TMM neglects Na+ ion effects on Me2+ ion binding ("condensation") to DNA. The results obtained show that in comparison with TMM the "ligand" theory describes more adequately DNA helix-coil transition in the presence of divalent metal ions in the region of both low and high ionic strengths of solution.
Subject(s)
DNA/chemistry , Nucleic Acid Conformation , Ligands , Models, BiologicalABSTRACT
UV differential spectroscopy is applied to study the interaction of Cu2+, Ni2+, Mn2+ ions with deoxyribonucleotides of canonic bases (dGMP, dAMP, dCMP, dTMP) and native DNA. Heteroatoms of the bases, coordinating ions, and binding constants which characterize the formation of metal complexes are found. The affinity of the ions is lower for the deoxyribonucleotide bases than for the ribonucleotide ones. This indicates that 02' of ribose participates in the stabilization of the metal complex even under conditions close to the neutral one (pH 6). Unlike the Cu2+ ions, Ni2+ and Mn2+ ions do not interact with N3C both in monomers and polymers. This seems to be the main factor explaining why copper makes DNA transform into a structure with a quasi-Hoogsteen pairing of GC pairs. No transformations of this kind of helix-coil transitions are caused by manganese and nickel up to concentrations 4 X 10(-2) M.
