The DNA-recognizing autoantibodies were prepared in milligram scale and their catalytic activities were investigated using various standard substrates for hydrolysis of natural biomolecules such as DNA, carbohydrates, and proteins. Only phosphatase and glycosidase activity was found and no peptidase, sulfatase, or esterase activity was detected in most of anti-DNA monoclonal autoantibodies we tested. Antibody G1-2 showed the highest catalytic activities and its enzymatic characteristics were further investigated. The antibody showed phosphatase activity with sub-millimolar substrate specificity and 10(4)-10(5) rate enhancements. However, Ab G1-2 showed low micro-molar specificity with p-nitrophenyl-beta-D-N-acetylglucosamide with 10(4)-10(5) rate enhancements. Both of the catalytic activities showed pH maximum at 4-5, suggesting that the carboxylate(s) in antigen-binding site is involved in the catalytic mechanism. Chemical protection of carboxylate(s) with diazoacetamide showed much reduced activity of the Ab, confirming that the catalytic activity comes from carboxylate(s) in the Ag-binding region. The activities of phosphatase and glycosidase were thoroughly inhibited by DNA with almost identical K(i) values. These data suggest that DNA-binding site(s) is the enzymatic active site of the catalytic Abs. Capabilities of the DNA recognition might make it possible to confer the Ab the catalytic activity of phosphate and glycosidic bond hydrolysis, which can be the main cause of DNA cleavage.