The nonenzymatic glycation of copper, zinc-superoxide dismutase (Cu,Zn-SOD) led to inactivation and fragmentation of the enzyme. The glycated Cu,Zn-SOD was isolated by boronate affinity chromatography. The formation of 8-hydroxy-2`-deoxyguanosine (B-OH-dG) in calf thymus DNA and the generation of strand breaks in pBluescript plasmid DNA by a metal-catalyzed oxidation (MCO) system composed of Fe^(3+), O₂, and glutathione (GSH) as an electron donor was enhanced more effectively by the glycated Cu,Zn-SOD than by the nonglycated enzyme. The capacity of glycated Cu,Zn-SOD to enhance damage to DNA was inhibited by diethylenetriaminepentaacetic acid (DETAPAC), azide, mannitol, and catalase. These results indicated that incubation of glycated Cu,Zn-SOD with GSH-MCO may result in a release of Cu^(2+) from the enzyme. The released Cu^(2+) then likely participated in a Fenton-type reaction to produce hydroxyl radicals, which may cause the enhancement of DNA damage.