reductases

Reductases are enzymes that catalyze reduction reactions, typically by transferring electrons or hydrogen to a substrate. They belong to the broader family of oxidoreductases (EC 1) and most often rely on electron donors such as NADH or NADPH. The substrates reduced by these enzymes range from simple carbonyl compounds to bulky xenobiotics, often with high regio- and stereoselectivity.

Mechanisms and cofactors: Reductases can utilize flavin cofactors such as FMN or FAD, or operate with flavin-independent hydride transfer from NADPH. Some reactions occur in partnership with cellular thiols, for example in glutathione-dependent redox systems. The resulting products are often alcohols, amines, or saturated bonds introduced by hydrogenation.

Representative enzyme families include aldo-keto reductases (AKR), carbonyl reductases (CBR), nitroreductases, azoreductases, and the Old Yellow Enzyme (OYE) family of FMN-dependent enzymes. Members of these families may show strict substrate preferences and can be engineered for altered cofactor specificity or activity.

Biological and practical roles: In cells, reductases participate in steroid and fatty acid metabolism, prostaglandin synthesis, and detoxification of xenobiotics. They are also exploited in biotechnology for enantioselective synthesis of chiral alcohols and other reduced products, and in pharmacology for investigating drug metabolism. Aberrant reductase activity can influence disease processes and drug resistance.