Hydrolysis of the deoxyribose N-glycosidic bond to excise 3-methyladenine or 7-methyladenine from the damaged DNA polymer formed by alkylation lesions. Can release ethylated and propylated bases from DNA in addition to 3-methyladenine. Hydrolysis of alkylated DNA, releasing 3-methyladenine, 3-methylguanine, 7-methylguanine and 7-methyladenine. Belongs to the alkylbase DNA glycosidase AlkA family.