**2.1 Production of anti-8-nitroguanine antibody**

Anti-8-nitroguanine polyclonal antibody was produced by a modified method (Akaike et al., 2003). 8-Nitroguanosine was incubated with sodium metaperiodate for 20 min at room temperature and then conjugated with rabbit serum albumin (RSA) for 1 h followed by incubation with sodium borohydride for 1 h. The conjugate was dialyzed against 150 mM NaCl overnight. 8-Nitroguanine–aldehyde–RSA conjugate mixed with Freund's complete adjuvant was injected in rabbit by intracutaneous administration. After 4 weeks of the immunization, the same antigen was given and the blood was taken two weeks later. We immobilized 8-nitroguanine in a cellulofine GCL-2000m column (Seikagaku Kogyo, Tokyo, Japan), and then purified the antibody by affinity chromatography.
