Influence of Copper2+ Ions on the Denaturation and Spectral Properties of DNA and Methylated DNA

Abstract

Further indications have been obtained for the complex binding site of Cu2+ with DNA from difference spectra and titration of methylated and non-methylated DNA-Cuz+ complexes.The ultraviolet spectra of GC-rich DNAs show a shift in their absorption maxima of approx. 3 nm in the presence of Cu2+. A more pronounced displacement of the maxima is observed in the difference spectra of DNA-Cue+ complexes depending on the GC content.Methylation of DNA a t N-7 of guanine reduces the afsnity of DNA for Cu2+ association: the destabilizing effect of Cue+ on melting of the double helix is markedly diminished, and difference spectra are less affected by Cuz+.Spectrophotometric titration of various DNAs indicates binding of Cu2+ to the bases a t low ionic strength and at 25". The Cuzf-induced hyperchromic change depends on the GC-content and is affected by specific methylation of guanine residues and by protonation of the GC pairs.The results are compared with literature data, and can be interpreted in terms of a coordination of Cu2+ with GC pairs: a resonable value for the binding of Cu2+ t o DNA at 25" appears to be 1 Cu2f per GC pair.I n the past years several investigators have shown that Cua+ ions may produce a drastic decrease in the helix stability of DNA against thermal denaturation when present at certain Cuz+ concentrations and at low ionic strength [i--8]. These aspects may be of biological interest, since it was shown that carefully isolated DNA samples contained specific amounts of copper and some other metals MATERIALS AND METHODSThe DNA samples used in this work are described elsewhere [17,18]. Nucleosides were purchased from Serva-Entwicklungslabor (Heidelberg), Fluka A. G., and Arcochemie (Berlin). Inorganic chemicals were reagent grade; for low ionic strength solutions sodium salts were used with impurities of divalent meta1 ions below 0.005 Ole.Methylated DNA was prepared according to the method of Pochon and Michelson [i9] with some modification. mi-n-butylamine and dimethyl sulphate were added as a mixture to the precooled DNA solution. The mixture was carefully shaken with ether to separate tri-n-butylamine after reaction;

DNA degradation by the mixture of copper and catechol is caused by DNA-copper-hydroperoxo complexes, probably DNA-Cu(I)OOH

“…Methylation of guanine N-7 inhibits the formation of a complex of Cu(II) with guanine and cytosine [Zimmer and Venner, 1970]. A similar effect on the formation of the Cu(I)-DNA complex was expected after the replacement of nitrogen-7 of guanine by a carbon atom.…”

Vibrational circular dichroism and IR absorption of DNA complexes with Cu2+ ions

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The binding of Cu 2ϩ -DNA is a highly cooperative process and is related to DNA denaturation that is similar to acid denaturation. 16 At very low metal concentrations, Cu 2ϩ binds nonspecifically to the phosphate groups like most of the other ions [ Fig.…”

Localization of the Slack potassium channel in the rat central nervous system

“…Because of the significance of Cu 2+ in biological processes, its interaction with nucleic acids has been studied extensively over several decades using different methods and techniques 1–19. The binding of Cu 2+ –DNA is a highly cooperative process and is related to DNA denaturation that is similar to acid denaturation 16.…”