Hydroxylation

Hydroxylation is a chemical process that introduces a hydroxyl group (-OH) into an organic compound. In biochemistry, hydroxylation reactions are often facilitated by enzymes called hydroxylases. Hydroxylation is the first step in the oxidative degradation of organic compounds in air. It is extremely important in detoxification since hydroxylation converts lipophilic compounds into water-soluble (hydrophilic) products that are more readily excreted. Some drugs (e.g. steroids) are activated or deactivated by hydroxylation.

Chemical concepts

The hydroxylation process involves conversion of a CH group into a COH group. Hydroxylation is an oxidative process. The oxygen that is inserted into the C-H bond is usually derived from atmospheric oxygen (O2). Since O2 itself is a slow hydroxylating agent, catalysts are required to accelerate the pace of the process.

Biological hydroxylation

The principal hydroxylation agent in nature is cytochrome P-450, hundreds of variations of which are known.Other hydroxylating agents include flavins.^[1]

Hydroxylation of proteins

The principal residue to be hydroxylated in proteins is proline. The hydroxylation occurs at the γ-C atom, forming hydroxyproline (Hyp), an essential element of collagen, in turn a necessary element of connective tissue. Proline hydroxylation is also a vital component of hypoxia response via hypoxia inducible factors. In some cases, proline may be hydroxylated instead on its β-C atom. Lysine may also be hydroxylated on its δ-C atom, forming hydroxylysine (Hyl).

These three reactions are catalyzed by very large, multi-subunit enzymes prolyl 4-hydroxylase, prolyl 3-hydroxylase and lysyl 5-hydroxylase, respectively. These reactions require iron (as well as molecular oxygen and α-ketoglutarate) to carry out the oxidation, and use ascorbic acid (vitamin C) to return the iron to its oxidized state. Deprivation of ascorbate leads to deficiencies in proline hydroxylation, which leads to less stable collagen, which can manifest itself as the disease scurvy. Since citrus fruits are rich in vitamin C, British sailors were given limes to combat scurvy on long ocean voyages; hence, they were called "limeys".

Examples of hydroxylases

• 17α-Hydroxylase
• Cholesterol 7 alpha-hydroxylase
• Dopamine β-hydroxylase
• Phenylalanine hydroxylase
• Tyrosine hydroxylase

References

1. ^ Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.

This protein-related article is a stub. You can help Wikipedia by expanding it.v · Categories: Organic redox reactions Proteins Posttranslational modification Protein stubs Wikimedia Foundation. 2010. Игры ⚽ Нужен реферат? BBB Ying Lianzhi Look at other dictionaries: hydroxylation — ● hydroxylation nom féminin Fixation de groupes hydroxyles sur une molécule organique. hydroxylation [idʀɔksilɑsjɔ̃] n. f. ÉTYM. 1906, in Rev. gén. des Sc. no 13, p. 621; de hydroxyle. ❖ ♦ Chim. organique. Fixation de groupes hydroxyle sur une… …   Encyclopédie Universelle Hydroxylation — L hydroxylation est une réaction chimique consistant à ajouter un groupement hydroxyle ( OH) à une molécule. Exemples de réactions d hydroxylation hydroxylation de la proline en hydroxyproline par une prolyl hydroxylase (enzyme). hydroxylation de …   Wikipédia en Français hydroxylation — hidroksilinimas statusas T sritis chemija apibrėžtis HO– grupės įjungimas į molekulę. atitikmenys: angl. hydroxylation rus. гидроксилирование …   Chemijos terminų aiškinamasis žodynas hydroxylation — noun see hydroxylate …   New Collegiate Dictionary hydroxylation — See hydroxylate. * * * …   Universalium hydroxylation — noun The introduction of a hydroxyl group into a molecule, especially by the replacement of a hydrogen atom …   Wiktionary hydroxylation — Placing of a hydroxyl group on a compound in a position where one did not exist before. * * * hy·drox·y·la·tion hī .dräk sə lā shən n the introduction of hydroxyl into an ion or radical usu. by the replacement of hydrogen hy·drox·y·late dräk sə… …   Medical dictionary hydroxylation — hy·drox·yl·ation …   English syllables hydroxylation — noun see hydroxylate …   Useful english dictionary Milas hydroxylation — The Milas hydroxylation is an organic reaction converting an alkene to a vicinal diol, and was developed by N. A. Milas in the 1930s.[1] The cis diol is formed by reaction of alkenes with hydrogen peroxide and either ultraviolet light or a… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”