Vitamin B7 And Biotin Deficiency

By Author: Abinash Mallick
Total Articles: 21
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Biotin, also known as vitamin H or coenzyme R,[2] is a water-soluble B-vitamin (vitamin B7).

It is composed of a ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a coenzyme for carboxylase enzymes, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis.

The only human health condition for which there is strong evidence of biotin's potential benefit as a treatment is biotin deficiency.

Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids. Biotin assists in various metabolic reactions involving the transfer of carbon dioxide. It may also be helpful in maintaining a steady blood sugar level.[4] Biotin is often recommended as a dietary supplement for strengthening hair and nails, though scientific data supporting this outcome are weak.[5][6] Nevertheless, biotin is found in many cosmetics and health products for the hair and skin.[7][8]

Biotin deficiency ...
... is rare because, in general, intestinal bacteria produce biotin in excess of the body's daily requirements.[9] For that reason, statutory agencies in many countries, for example the USA[10] and Australia,[11] do not prescribe a recommended daily intake of biotin. However, a number of metabolic disorders exist in which an individual's metabolism of biotin is abnormal, such as deficiency in the holocarboxylase synthetase enzyme which covalently links biotin onto the carboxylase, where the biotin acts as a cofactor.

Biotin has an unusual structure (see above figure), with two rings fused together via one of their sides. The two rings are ureido and thiophene moieties. Biotin is a heterocyclic, S-containing monocarboxylic acid. It is made from two precursors, alanine and pimeloyl-CoA via three enzymes. 8-Amino-7-oxopelargonic acid synthase is a pyridoxal 5'-phosphate enzyme. The pimeloyl-CoA, could be produced by a modified fatty acid pathway involving a malonyl thioester as the starter. 7,8Diaminopelargonic acid (DAPA) aminotransferase is unusual in using S-adenosyl methionine (SAM) as the NH2 donor. Dethiobiotin synthethase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP. Biotin synthase reductively cleaves SAM into a deoxyadenosyl radical—a first radical formed on dethiobiotin is trapped by the sulfur donor, which was found to be the iron-sulfur (Fe-S) center contained in the enzyme.

Biotin is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. It covalently attaches to the epsilon-amino group of specific lysine residues in these carboxylases. This biotinylation reaction requires ATP and is catalyzed by holocarboxylase synthetase.[14] In bacteria, biotin is attached to biotin carboxyl carrier protein (BCCP) by biotin protein ligase (BirA in E. coli).[15] The attachment of biotin to various chemical sites, biotinylation, is used as an important laboratory technique to study various processes, including protein localization, protein interactions, DNA transcription, and replication. Biotinidase itself is known to be able to biotinylate histone proteins,[16] but little biotin is found naturally attached to chromatin.

For more information please visit: http://en.wikipedia.org/wiki/Biotin