monooxygénases

Monooxygénases, or monooxygenases, are enzymes that catalyze the incorporation of one atom of molecular oxygen into an organic substrate while the second oxygen atom is reduced to water. They form a diverse family within the oxidoreductases and typically require reducing equivalents (for example NADPH or NADH) delivered through partner proteins or cofactors. Their active centers include heme in cytochrome P450 enzymes, flavin cofactors in flavin-containing monooxygenases, and various metal centers in other families.

Most monooxygénases activate O2 at these centers to form reactive intermediates that insert one oxygen atom into the substrate with high regio- and stereoselectivity. In cytochrome P450 enzymes, electrons are transferred from NADPH via a reductase to the heme center to drive oxygen insertion. Flavin-containing monooxygenases operate via a flavin-hydroperoxide intermediate derived from NADPH. Methane monooxygenase and related bacterial enzymes illustrate the diversity of the class beyond drug metabolism.

Biological roles are broad: in animals, monooxygénases metabolize and detoxify xenobiotics, participate in steroid and drug metabolism, and contribute to biosynthetic pathways for hormones and signaling molecules. In plants and microbes, monooxygénases generate secondary metabolites and degrade environmental pollutants. They are also exploited in biocatalysis and pharmaceutical synthesis to perform selective oxidations that are difficult to achieve chemically.

Structure and localization vary: eukaryotic cytochrome P450s are typically membrane-associated, whereas FMOs are soluble cytosolic enzymes. Bacterial monooxygénases include soluble enzymes such as methane monooxygenase that target alkanes. Regulation of monooxygénases is closely tied to substrate availability, cofactor supply, and cellular redox state.