Flavin-Containing Monooxygenases in Drug Metabolism and Genetic Variability

Flavin-containing monooxygenases (FMOs) constitute a conserved family of enzymes that catalyse the oxygenation of a broad spectrum of drugs, dietary compounds and environmental chemicals. By forming a C4a-hydroperoxyflavin intermediate, they facilitate the detoxification or activation of heteroatom-containing substrates, thereby shaping pharmacokinetic profiles and influencing drug efficacy and safety. Five major mammalian isoforms (FMO1–FMO5) display distinct tissue distributions and substrate preferences, while genetic polymorphisms—most notably within FMO3—give rise to interindividual variability in drug clearance and predisposition to metabolic conditions such as trimethylaminuria. An evolutionary perspective reveals that only a few key amino acid substitutions are required to shift FMO function from promiscuous ancestral enzymes to specialised monooxygenases, underscoring the delicate balance between enzyme flexibility and specificity. The interplay of FMO genetics, expression patterns and chemical exposure has broad implications for personalised medicine, toxicology and public health.

Research from Nature Portfolio

Recent studies have traced the molecular evolution of FMOs by reconstructing ancestral sequences and identifying the minimal set of substitutions that conferred specialised monooxygenase activity in tetrapods. This work showed that mutations distant from the active site modulate the stability and reactivity of the flavin hydroperoxide intermediate, thereby directing substrate selectivity. In parallel, structural and kinetic analyses of a human FMO3 polymorphic variant revealed the mechanistic basis for loss of function: substitution of a single residue in the NADPH-binding site disrupts flavin stabilisation, accelerates hydroperoxide decay and reduces oxygen transfer to multiple substrates. These advances link evolutionary diversification with genetic variability, offering a unified framework for understanding how small sequence changes can profoundly alter drug-metabolising capacity.

Flavin-Containing Monooxygenases in Drug Metabolism and Genetic Variability publication trend

The graph below shows the total number of articles in flavin-containing monooxygenases in drug metabolism and genetic variability across all publications each year (not limited to Nature Index journals).

Technical terms

Flavin-Containing Monooxygenase (FMO): An NADPH-dependent enzyme that oxygenates heteroatom-containing substrates via a flavin hydroperoxide intermediate.

Xenobiotic: A chemical compound foreign to an organism, including drugs and environmental toxins.

Trimethylamine N-oxide (TMAO): The oxidised product of trimethylamine generated primarily by FMO3, linked to metabolic and cardiovascular outcomes.

Polymorphism: A heritable genetic variation that can alter enzyme structure or activity, affecting individual responses to xenobiotics.

NADPH: Nicotinamide adenine dinucleotide phosphate; a reducing cofactor that donates electrons for FMO-catalysed oxygenation reactions.

References

1. Evolution of enzyme functionality in the flavin-containing monooxygenases. Nature Communications (2023).
2. Inactivation mechanism of N61S mutant of human FMO3 towards trimethylamine. Scientific Reports (2017).
3. Living with trimethylaminuria and body and breath malodour: personal perspectives. BMC Public Health (2024).
4. Flavin-Containing Monooxygenases Are Conserved Regulators of Stress Resistance and Metabolism. Frontiers in Cell and Developmental Biology (2021).
5. Reactions of the 4a-hydroperoxide of liver microsomal flavin-containing monooxygenase with nucleophilic and electrophilic substrates.. Journal of Biological Chemistry (1986).