Acts as Baeyer-Villiger monooxygenase on a broad range of substrates. Catalyzes the insertion of an oxygen atom into a carbon-carbon bond adjacent to a carbonyl, which converts ketones to esters. Active on diverse carbonyl compounds, whereas soft nucleophiles are mostly non- or poorly reactive. In contrast with other forms of FMO it is non- or poorly active on 'classical' substrates such as drugs, pesticides, and dietary components containing soft nucleophilic heteroatoms. Able to oxidize drug molecules bearing a carbonyl group on an aliphatic chain, such as nabumetone and pentoxifylline. Also, in the absence of substrates, shows slow but yet significant NADPH oxidase activity (By similarity). Acts as a positive modulator of cholesterol biosynthesis as well as glucose homeostasis, promoting metabolic aging via pleiotropic effects (PubMed:26049045, PubMed:28646079). H(+) + N,N-dimethylaniline + NADPH + O2 = H2O + N,N-dimethylaniline N-oxide + NADP(+) H(+) + NADPH + O2 = H2O2 + NADP(+) H(+) + heptan-2-one + NADPH + O2 = H2O + NADP(+) + pentyl acetate H(+) + NADPH + O2 + octan-3-one = H2O + NADP(+) + pentyl propanoate H(+) + NADPH + O2 + octan-3-one = ethyl hexanoate + H2O + NADP(+) H(+) + hexan-3-one + NADPH + O2 = ethyl butanoate + H2O + NADP(+) H(+) + hexan-3-one + NADPH + O2 = H2O + NADP(+) + propyl propanoate H(+) + heptan-4-one + NADPH + O2 = H2O + NADP(+) + propyl butanoate (2E)-geranial + H(+) + NADPH + O2 = (1E)-2,6-dimethylhepta-1,5-dien-1-yl formate + H2O + NADP(+) H(+) + NADPH + O2 + sulcatone = 4-methylpent-3-en-1-yl acetate + H2O + NADP(+) Expressed in liver (at protein level) (PubMed:26049045). Expressed in the mucosal epithelium of the gastrointestinal tract (PubMed:28646079). In the gastrointestinal tract, expression is induced in response to a high-fat diet. Mutants exhibit a lean phenotype, which is age-related, becoming apparent after 20 weeks of age. Despite greater food intake, they weigh less, store less fat in white adipose tissue (WAT), have lower plasma glucose and cholesterol concentrations and enhanced whole-body energy expenditure, due mostly to increased resting energy expenditure, with no increase in physical activity. They show a a higher rate of fatty acid oxidation in WAT (PubMed:26049045, PubMed:29686991). When fed a high-fat diet, they are protected against weight gain and reduction of insulin sensitivity (PubMed:28646079). Belongs to the FMO family.