A role of iron in lambda DNA strand breaks in the reaction system of alloxan with reduced glutathione: iron(III) binding to the DNA.

lambda DNA strand breaks were easily induced in a reaction system involving alloxan with reduced glutathione (GSH) in the presence of FeCl3 in a HEPES-NaOH buffer, pH 7.4. Increasing concentrations of FeCl3 in the reaction system caused DNA strand breaks in a concentration-dependent fashion, suggesting that iron is required to induce the DNA strand breaks. Catalase, scavengers of hydroxyl radicals (HO.) and iron-chelators almost completely inhibited the DNA strand breaks, but superoxide dismutase (SOD) did not do so, suggesting that the HO., formed by a Fenton-type reaction, was the species responsible for the DNA strand breaks. The addition of FeCl3 to the solution containing DNA caused the formation of a DNA-Fe(III) complex, in which Fe(III) was reduced by an alloxan radical (HA.) but not by a superoxide radical. Only when apotransferrin was added to the reaction mixtures before the addition of FeCl3, were both the DNA strand breaks and the reduction of Fe(III) strongly inhibited. These results suggest that the Fe(III) bound to DNA catalyzes the DNA strand breaks which may be caused by the generation of site-specific HO. via an HA.-dependent Fenton-type reaction.