DNA damage in the photocatalysis system of TiO₂ and the effect of SOD were studied using calf thymus DNA as research object. The degree of DNA damage was detected by gel electrophoresis and high performance liquid chromatography (HPLC) analysis. 8-Hydroxy-2 -deoxyguanosine (8-OHdG) was used as an internal standard, HPLC-ESI-MS/MS were employed to analyze products of DNA damage. Peroxidase catalytic spectrophotometry and electron spin resonance (ESR) were used to determine the content of H₂O₂ and the change of reactive oxygen species, the mechanism of DNA damage was studied. The results indicated that the degree of DNA damage in different systems was in the order of UV/TiO₂＞UV＞Dark/TiO₂, the degree of DNA damage reached 99% after 260 min and the reaction kinetic constants K was equal to 7.82×10^－3 min^－1. SOD used as an antioxidant had the ability of removing free radicals and inhibiting DNA damage, the reaction kinetic constants K was equal to 2.27×10^－3 min^－1 in the system with SOD. 8-OHdG was the special product of guanine damage. DNA damage process was predominated mainly by the hydroxyl radical (•OH) and superoxide radical ( ) generated in the system. Besides, photocatalytic damage was with the mineralization of DNA and mineralization rate reached 75.06% after 12 h.

Key words: calf thymus DNA, DNA damage, photocatalysis, superoxide dismutase