4-methylaminobutanoate oxidase (methylamine-forming) (, mao (gene)) is an enzyme with systematic name 4-methylaminobutanoate methylamidohydrolase. This enzyme catalyses the following chemical reaction
The enzyme participates in the nicotine degradation in soil bacterium Arthrobacter nicotinovorans. This bacterium also contains the enzyme 4-methylaminobutanoate oxidase (formaldehyde-forming), which gives ó-aminobutyric acid and formaldehyde as its products, rather than succinic semialdehyde and methylamine.