Interaction of Mn2+ with DNA as studied by proton‐relaxation enhancement of solvent water

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Abstract
The binding of Mn2+ to double‐stranded DNA in solution has been studied by measuring the proton‐relaxation enhancement of solvent water. The nmr experiments were carried out on DNAs of different base composition and showed the existence of weak and tight binding sites for Mn2+. The former sites are related to the electrostatic binding of the divalent cation with two contiguous phosphate groups, and the latter appear to vary almost proportionally with the number of G·C base pairs in the DNAs. Our results agree, in general, with the emerging evidence for a specific interaction of Mn2+ with the G·C residues of DNA. Competition experiments with Mg2+ suggested that this binding of Mn2+ in DNA also involves the phosphate groups. More definitely, our data conform with the hypothesis made by Clement et al. of Mn2+ chelation between the phosphate and the nitrogen N7 of a deoxyguanyl unit of DNA.