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Hydroxylation

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Title: Hydroxylation  
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Subject: Protein primary structure, Amino acid, Medrogestone, Carnitine biosynthesis, 21-Hydroxylase
Collection: Organic Redox Reactions, Posttranslational Modification, Proteins
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Hydroxylation

Hydroxylation is a steroids) are activated or deactivated by hydroxylation.

Contents

  • Chemical concepts 1
  • Biological hydroxylation 2
  • Hydroxylation of proteins 3
  • Examples of hydroxylases 4
  • References 5

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

References

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