Flavin-containing monooxygenase 3 (FMO3), also known as dimethylaniline monooxygenase [N-oxide-forming] 3 and trimethylamine monooxygenase, is a flavoprotein enzyme (EC 1.14.13.148) that in humans is encoded by the FMO3 gene.[5][6][7][8]
This enzyme catalyzes the following chemical reaction, among others:[8]
- trimethylamine + NADPH + H+ + O2 trimethylamine N-oxide + NADP+ + H2O
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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).[9][12]
FMO3 is the primary enzyme in humans which catalyzes the N-oxidation of trimethylamine into trimethylamine N-oxide;[8][10] FMO1 also does this, but to a much lesser extent than FMO3.[13][14] Genetic deficiencies of the FMO3 enzyme cause primary trimethylaminuria, also known as "fish odor syndrome".[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]