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

The effect of Cr²⁺ ions on the T_m (melting temperature) of DNA has been investigated under appropriate conditions for the stabilization of DNA by Mg²⁺ ions. A significant lowering of T_m, 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 T_m 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.