FMO5

FMO5, or flavin-containing monooxygenase 5, is an enzyme in the flavin-containing monooxygenase (FMO) family. Like other FMOs, FMO5 is a flavoprotein that uses NADPH and molecular oxygen to oxidize a range of soft nucleophiles, typically introducing an oxygen atom to sulfides and amines to form sulfoxides and amine oxides. This activity supports the metabolism and detoxification of xenobiotics and some endogenous substrates in vertebrates.

In humans, FMO5 is predominantly expressed in the liver and kidney, with lower levels in other tissues. FMOs are generally microsomal enzymes localized to the endoplasmic reticulum, where they participate in oxidative metabolism of diverse compounds.

FMO5 displays substrate preferences that can differ from other family members, and its contribution to overall metabolism can be variable and tissue- or species-specific. For many substrates, FMO3 is the dominant enzyme, while FMO5 contributes to the metabolism of others, reflecting the distinct roles of FMO isoforms in xenobiotic handling.

Physiological and genetic insights come from model organisms. In mice, FMO5 influences energy metabolism and adiposity; Fmo5 knockout mice show reduced adiposity and increased energy expenditure, suggesting a role in metabolic regulation beyond xenobiotic oxidation. In humans, the precise physiological function is less clearly defined, but genetic variation in FMO5 can affect enzyme activity and may contribute to interindividual differences in drug metabolism.

Clinical relevance and research focus on FMO5 center on its role in drug disposition and toxicology, its regulation, and its potential involvement in metabolic traits, alongside the better-characterized FMO1–3 enzymes.