Biotin

Biotin
General
Chemical formula	C10H16N2O3S
Molecular weight	244.31 g/mol
Other names
Vitamin B7 Vitamin H
Vitamin properties
Solubility	Water
RDA (adult male)	30 μg/day
RDA (adult female)	30 μg/day
RDA upper limit (adult male)	None
RDA upper limit (adult female)	None
Deficiency symptoms
Dry scaly skin Fatigue Loss of appetite Nausea and vomiting Mental depression Tongue inflammation High cholesterol
Excess symptoms
None
Common sources
Liver and kidney Dairy products Some seafood, especially oysters, lobster, and salmon Yeast Cauliflower Chicken breast Egg yolk (but not egg white)

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 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. It is commonly found in pyruvate dehydrogenase as a carrier of HCO₃^-.

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.

Cradle cap (seborrheic dermatitis)

Children with a rare inherited metabolic disorder called phenyulketonuria (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.

Initial symptoms of biotin deficiency include:

1. Dry skin
2. Seborrheic dermatitis
3. Fungal infections
4. Rashes including erythematous periorofacial macular rash
5. Fine and brittle hair
6. Hair loss or total alopecia

If left untreated, neurological symptoms can develop, including:

1. Mild depression, which may progress to profound lassitude and, eventually, to somnolence
2. Changes in mental status
3. Generalized muscular pains (myalgias)
4. Hyperesthesias and paresthesias

The treatment for biotin deficiency is to simply start taking some biotin supplements.

Biochemistry

Biotin is a cofactor responsible for carbon dioxide transfer in several carboxylase enzymes:

• Acetyl-CoA carboxylase
• Methylcrotonyl-CoA carboxylase
• Propionyl-CoA carboxylase
• Pyruvate carboxylase

The attachment of biotin to various proteins, called biotinylation, is an important process in DNA transcription and replication.

Biotin binds very tightly to the tetrameric protein streptavidin, with a dissociation constant K_d in the order of 10^-14M. This is often used in different biotechological applications. Until 2005, very harsh conditions were required to break the biotin-streptavidin bond (Holmberg et al, 2005).

References

• The biotin-streptavidin interaction can be reversibly broken using water at elevated temperatures, Holmberg, A. et al Electrophoresis 2005, 26(3), 501-10.
• Article on Biotin deficiency by Dr. Howard R Sloan

See also

• Biotinylation

External links

• Oregon State University