Hydrolysis of the deoxyribose N-glycosidic bond to excise 3-methyladenine or 7-methyladenine from the damaged DNA polymer formed by alkylation lesions. Hydrolysis of alkylated DNA, releasing 3-methyladenine, 3-methylguanine, 7-methylguanine and 7-methyladenine. By DNA damage. Belongs to the alkylbase DNA glycosidase AlkA family.