The role of the superoxide and hydroxyl radicals in the degradation of DNA and deoxyribose induced by a copper-phenanthroline complex.

DNA degradation by a copper(II)-phenanthroline complex was studied in the presence of NADH, 2-mercaptoethanol or a mixture of hypoxanthine and xanthine oxidase, which generates the superoxide radical, O2-. In all cases degradation was prevented by catalase but not by scavengers of the hydroxyl radical, OH. It remains possible, however, that OH was generated in close association with DNA so that the scavengers could not remove it before it reacted. Superoxide dismutase inhibited DNA degradation at low copper (II) phenanthroline concentrations in the presence of NADH or hypoxanthine-xanthine oxidase, but not at higher complex concentrations. Superoxide dismutase had little effect on DNA degradation in the presence of 2-mercaptoethanol. The role of oxygen radicals in the DNA degradation induced by copper(II) phenanthroline is discussed.