Denaturation of DNA in the presence of chromous (Cr2+) ions

The effect of Cr2+ ions on the Tm (melting temperature) of DNA has been investigated under appropriate conditions for the stabilization of DNA by Mg2+ ions. A significant lowering of Tm, analogous to that observed for Cu2+ under normal conditions, was found, for Cr2+ at pH = 4.2 and [Mg2+] = 5.3 mol per mole of DNA base pair. Cu2+ also lowers Tm under similar conditions. The similarity of the effects of Cr2+ and Cu2+ under comparable conditions may be related to similarities in their coordination properties. It is proposed that Cr2+ and Cu2+ ions facilitate denaturation by holding together groups on the DNA chains in such a manner that base pairing and base stacking are inhibited. Comparative results for Cr3+ and Co2+ are also given for these low pH/Mg2+ ion conditions.