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Biotin

Biotin, also known as vitamin H or B₇ and C₁₀H₁₆N₂O₃S (Biotin; Coenzyme R, Biopeiderm), is a water-soluble B-complex vitamin which is composed of an 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 important in the catalysis of essential metabolic reactions to synthesize fatty acids, in gluconeogenesis, and to metabolize leucine. more...

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General overview

Biotin is used in cell growth, the production of fatty acids, metabolism of fats, and amino acids. It plays a role in the Krebs Cycle, which is the process in which energy is released from food. Biotin not only assists in various metabolic chemical conversions, but also helps with the transfer of carbon dioxide. Biotin is also helpful in maintaining a steady blood sugar level. Biotin is often recommended for strengthening hair and nails. Consequently, it is found in many cosmetic and health products for the hair and skin.

Uses

Hair problems

Biotin supplements are often recommended as a natural product to counteract the problem of hair loss in both children and adults. However, there are no studies that show any benefit in any case where the subject is not actually biotin deficient. The signs and symptoms of biotin deficiency include hair loss which progresses in severity to include loss of eye lashes and eye brows in severely deficient subjects. Of note, shampoos that include biotin might be more effective if they were drunk instead of poured over the head as the absorption of biotin through the skin is limited (but drinking shampoo might cause other problems that would offset any hair growth benefit).

Cradle cap (seborrheic dermatitis)

Children with a rare inherited metabolic disorder called phenylketonuria (PKU; in which one is unable to break down the amino acid phenylalanine) often develop skin conditions such as eczema and seborrheic dermatitis in areas of the body other than the scalp. The scaly skin changes that occur in people with PKU may be related to poor ability to use biotin. Increasing dietary biotin in the diet has been known to improve seborrheic dermatitis in these cases.

Diabetes

People with type 2 diabetes often have low levels of biotin. Biotin may be involved in the synthesis and release of insulin. Preliminary studies in both animals and people suggest that biotin may help improve blood sugar control in those with diabetes, particularly type 2 diabetes.

Biotin deficiency

Biotin deficiency is a rare nutritional disorder caused by a deficiency of biotin. Biotin deficiency can have a very serious, even fatal, outcome if it is allowed to progress without treatment. Signs and symptoms of biotin deficiency can develop in persons of any age, race, or gender. Biotin deficiency rarely occurs in healthy individuals, since the daily requirements of biotin are low, many foods contain adequate amounts, intestinal bacteria synthesize small amounts, and the body effectively scavenges and recycles biotin from bodily waste. However, deficiency can be caused by excessive consumption of raw egg-whites over a long period (months to years). Egg-whites contain high levels of avidin, a protein that binds biotin stongly. Once a biotin-avidin complex forms, the bond is essentially irreversible. The biotin-avidin complex is not broken down nor liberated during digestion, and the biotin-avidin complex is lost in the feces. Once cooked, the egg-white avidin becomes denatured and entirely non-toxic.

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Dissecting streptavidin-biotin interaction with a laminar flow chamber
From Biophysical Journal, 6/1/02 by Pierres, Anne

ABSTRACT A laminar flow chamber was used to study single molecule interactions between biotinylated surfaces and streptavidin-coated spheres subjected to a hydrodynamic drag lower than a piconewton. Spheres were tracked with 20 ms and 40 nm resolution. They displayed multiple arrests lasting between a few tens of milliseconds and several minutes or more. Analysis of about 500,000 positions revealed that streptavidin-biotin interaction was multiphasic: transient bound states displayed a rupture frequency of 5.3 s^sup -1^ and a rate of transition toward a more stable configuration of 1.3 s^sup -1^. These parameters did not display any significant change when the force exerted on bonds varied between 3.5 and 11 pN. However, the apparent rate of streptavidin-biotin association exhibited about 10-fold decrease when the wall shear rate was increased from 7 to 22 s^sup -1^, which supports the existence of an energy barrier opposing the formation of the transient binding state. It is concluded that a laminar flow chamber can yield new and useful information on the formation of molecular bonds, and especially on the structure of the external part of the energy landscape of ligand-receptor complexes.

INTRODUCTION

A major property of biomolecules is to bind a variety of ligands in order to fulfill a specific function such as mediating cell adhesion, triggering receptor-mediated cell activation or regulating intracellular networks. During the last decades, it became clear that simple parameters such as affinity or kinetic association and dissociation constants did not fully account for the binding behavior of cell receptors (Bell, 1978). Thus, the capture of flowing leukocytes by activated endothelium probably requires molecular associations endowed with especially high mechanical strength (Lawrence and Springer, 1991). The uptake of soluble ligands by surface-bound molecules is probably dependent on molecular length and flexibility (Pierres et al., 1998a). The recognition by T lymphocytes of complexes formed between major histocompatibility complex molecules and antigenic peptides may be influenced by transient conformational changes of these complexes (Anderson and McConnell, 1999).

This work was supported in part by a ministerial grant (Bioinformatics Programme).

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Anne Pierres, Dominique Touchard, Anne-Marie Benoliel, and Pierre Bongrand

Laboratoire d'Immunologie, INSERM U 387, Hopital Ste-Marguerite, BP 29, 13274 Marseille Cedex 09, France

Submitted September 10, 2001, and accepted for publication March 6, 2002.

Address reprint requests to Pr. Pierre Bongrand, Laboratoire d'Immunologie, INSERM U. 387, Hopital Ste-Marguerite, BP 29, 13274 Marseille Cedex 09, France. Tel.: 33-491-26-03-31; Fax: 33-491-75-73-28; E-mail: bongrand@marseille.inserm.fr.

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