Epoxidases

Epoxidases are enzymes that catalyze the formation of epoxides, three-membered cyclic ethers, by inserting one atom of oxygen into carbon–carbon double bonds (alkenes). The reaction, epoxidation, converts alkenes into reactive epoxides and plays a central role in metabolism, biosynthesis of natural products, and synthetic biocatalysis.

Most biological epoxidations are carried out by oxygenase systems that require an electron donor and molecular oxygen. Cytochrome P450 monooxygenases use NADPH (or NADH) to transfer electrons, activating O2 and delivering one oxygen atom to the substrate to form the epoxide, with water as a byproduct. Flavin-containing monooxygenases use flavin cofactors to perform a similar chemistry. Some enzymes, known as peroxygenases, can use hydrogen peroxide directly as the oxygen source, bypassing the need for NADPH.

Substrates for epoxidases include a wide range of alkenes such as fatty acids, terpenes, and various xenobiotic compounds. In plants and microorganisms, epoxidases contribute to the formation of signaling molecules, defense compounds, and detoxification products. Epoxidation can alter the reactivity and biological activity of substrates, enabling subsequent transformations.

Notable examples include bacterial styrene monooxygenase, which epoxidizes styrene to styrene oxide, and plant or fungal cytochrome P450 enzymes that epoxidize diverse double bonds in terpenoids and fatty acids. Epoxidases are also exploited in biocatalysis for selective epoxide synthesis in pharmaceutical and agrochemical manufacturing.

Terminology varies; the term epoxidase is often used for enzymes that catalyze epoxidation, particularly oxygenases in P450 and related families, but exact classification depends on the specific enzyme mechanism and cofactor involved.