Flavin Containing Monooxygenase 4 (FMO4)

Metabolic N-oxidation of the diet-derived amino-trimethylamine (TMA) is mediated by flavin-containing monooxygenase and is subject to an inherited FMO3 polymorphism in man resulting in a small subpopulation with reduced TMA N-oxidation capacity resulting in fish odor syndrome Trimethylaminuria. Three forms of the enzyme, FMO1 found in fetal liver, FMO2 found in adult liver, and FMO3 are encoded by genes clustered in the 1q23-q25 region. The cDNA encodes a deduced 558-amino acid protein with a molecular mass of 63,338 Da. FMO2 shows 51 to 53% primary sequence identity with FMO1. The corresponding mRNA was present in low abundance in adult human liver. Southern blot hybridization with single exon probes demonstrated that human FMO4 and FMO1 are, in each case, the product of a single gene.