 Though the enzyme uses molecular oxygen as an electron acceptor, the oxygen atom that is incorporated into the carboxylate product is from water; however, the exact mechanism of reduction is still not known for AO.The AO also catalyzes the oxidation of heterocycles, which involves a nucleophilic attack located at the carbon atom beside the heteroatom.This means that susceptibility to nucleophilic attack of a heterocycle determines if that heterocycle is a suitable substrate for AO.