[5][6][7][8] This enzyme catalyzes the following chemical reaction, among others:[8] FMO3 is the main flavin-containing monooxygenase isoenzyme that is expressed in the liver of adult humans.

[8][9][10] The human FMO3 enzyme catalyzes several types of reactions, including: the N-oxygenation of primary, secondary, and tertiary amines;[9][11] the S-oxygenation of nucleophilic sulfur-containing compounds;[9][11] and the 6-methylhydroxylation of the anti-cancer agent dimethylxanthenone acetic acid (DMXAA).

[8][15] FMO3 is also involved in the metabolism of many xenobiotics (i.e., exogenous compounds which are not normally present in the body),[9][10] such as the oxidative deamination of amphetamine.

[9][16][17] The FMO3 gene has been observed progressively downregulated in human papillomavirus-positive neoplastic keratinocytes derived from uterine cervical preneoplastic lesions at different levels of malignancy.

[20] For this reason, FMO3 is likely to be associated with tumorigenesis and may be a potential prognostic marker for progression of uterine cervical preneoplastic lesions.