Oxidation of aldehydes catalyzed by pig liver flavin-containing monooxygenase

Flavin-containing monooxygenase-1 (FMO1) purified to homogeneity from pig liver microsomes catalyzes NADPH- and oxygen-dependent oxidation of salicylaldehyde to pyrocatechol and formate. These products, formed in equimolar amounts, were the only ones detected that suggests that FMO1 catalyzes the oxidation of salicylaldehyde by Baeyer-Villiger chemistry. In addition to salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 5-chlorosalicylaldehyde, 5-nitrosalicylaldehyde, ferrocene carboxaldehyde, 2-pyridine carboxaldehyde, and acetylacetone also stimulated NADPH-dependent oxygen uptake in the presence of FMO1. On the other hand, benzaldehyde, 2-methoxybenzaldehyde, 4-pyridine carboxaldehyde and 3- or 4-hydroxybenzaldehyde, and none of the alkylaldehydes tested had detectable substrate activity. Pig liver FMO1 apparently only catalyzes C-oxidation of reactive aldehydes with a hydrogen ion acceptor function adjacent to the carbonyl.