hydroxylases

Hydroxylases are enzymes that catalyze the introduction of a hydroxyl group (-OH) into organic substrates, typically using molecular oxygen. They are a broad class within the oxidoreductases and play key roles in metabolism, biosynthesis, and detoxification.

There are two main types: monooxygenases, which insert one oxygen atom into the substrate and reduce the other oxygen to water, and dioxygenases, which incorporate both atoms of O2 into the substrate. Monooxygenases often rely on electron transfer proteins and cofactors such as NADPH, FAD, or heme groups; cytochrome P450 enzymes are the best-known family. Dioxygenases include enzymes such as lipoxygenases, which oxygenate fatty acids, and catechol dioxygenases, which cleave aromatic rings after hydroxylation. A major subfamily of dioxygenases is the 2-oxoglutarate-dependent oxygenases, which require Fe(II) and 2-oxoglutarate as co-substrates and convert substrates via hydroxylation; collagen prolyl hydroxylase is a well-known example.

Biological roles include synthesis and modification of hormones and vitamins, activation or detoxification of xenobiotics, and structural protein assembly (e.g., collagen). In bacteria and fungi, hydroxylases enable degradation and assimilation of difficult substrates, such as aromatic compounds.

Industrial and biomedical relevance: hydroxylases are studied as biocatalysts for regio- and stereoselective hydroxylation, aiding drug metabolism studies and the synthesis of complex molecules. Regulation of these enzymes can be influenced by oxygen levels and the presence of inducers.