Occurrence of flavin-containing monooxygenases in non-mammalian eukaryotic organisms

Flavin-containing monooxygenases (FMOs) have been identified in various organisms from bacteria to humans. However, because of the importance of these enzymes in the biotransformation of xenobiotics, the majority of studies have focused almost entirely upon the mammalian forms of the enzyme. Consequently, this review is an attempt to document the occurrence of FMO expression (mRNA, proteins, activities) in non-mammalian species in an attempt to provide insight about its putative physiological and toxicological roles. Activity indicative of FMO has been observed in numerous invertebrate species but corresponding proteins or transcripts have not been identified. There is a significant gap of information pertaining to insects, echinoderms, avian, reptilian and amphibian species. Significant homology of structure and function is observed in lower vertebrates. Evidence is provided primarily from studies with piscine forms of the enzyme suggesting a possible osmoregulatory role of FMOs, especially in euryhaline species of fish.