4-methylaminobutanoate oxidase (formaldehyde-forming) (, mabO (gene)) is an enzyme with systematic name 4-methylaminobutanoate:oxygen oxidoreductase (formaldehyde-forming). This enzyme catalyses the following chemical reaction
This enzyme is a flavoprotein containing flavin adenine dinucleotide. It is involved in the metabolism of nicotine in Arthrobacter nicotinovorans.