Aldehyde oxidase (AO) is a metabolizing enzyme, located in the cytosolic compartment of tissues in many organisms. AO catalyzes the oxidation of aldehydes into carboxylic acid, and in addition, catalyzes the hydrozylation of some heterocycles.[1] It can also catalyze the oxidation of both cytochrome P450 (CYP450) and monoamine oxidase (MAO) intermediate products. AO plays a very important role in the metabolization of numerous drugs.