AUTHOR Dr. Carlos Orozco (BSc, MSc, ND, MD, PhD, FPAMS).
Biotin is a water-soluble vitamin, generally classified as a B-complex vitamin. After the initial discovery of biotin, nearly forty years of research were required to establish it as a vitamin. Biotin is required by all organisms but can only be synthesized by bacteria, yeasts, molds, algae, and some plant species.
In its physiologically active form biotin is attached at the active site of four important enzymes, known as carboxylases . Each carboxylase catalyzes an essential metabolic reaction.
Acetyl-CoA carboxylase catalyzes the binding of bicarbonate to acetyl-CoA to form malonyl-CoA. Malonyl-CoA is required for the synthesis of fatty acids.
Pyruvate carboxylase is a critical enzyme in gluconeogenesis, the formation of glucose from sources other than carbohydrates, for example, amino acids and fats.
Methylcrotonyl-CoA carboxyla se catalyzes an essential step in the metabolism of leucine, an indispensable (essential) amino acid.
Propionyl-CoA carboxylase catalyzes essential steps in the metabolism of amino acids, cholesterol, and odd chain fatty acids (fatty acids with an odd number of carbon molecules).
Histones are proteins that bind to DNA and package it into compact structures to form chromosomes. The compact packaging of DNA must be relaxed somewhat for DNA replication and transcription to occur. Modification of histones through the attachment of acetyl or methyl groups (acetylation or methylation) has been shown to affect the structure of histones, thereby affecting replication and transcription of DNA. The attachment of biotin to another molecule, such as a protein, is known as “biotinylation”. The enzyme biotinidase has recently been shown to catalyze the biotinylation of histones, suggesting that biotin may play a role in DNA replication and transcription.
Signs and Symptoms of Deficiency
Although biotin deficiency is very rare, the human requirement for dietary biotin has been demonstrated in two different situations: prolonged intravenous feeding without biotin supplementation and consumption of raw egg white for a prolonged period (many weeks to years). Avidin is a protein found in egg white, which binds biotin and prevents its absorption. Cooking egg white denatures avidin, rendering it susceptible to digestion, and unable to prevent the absorption of dietary biotin.
Symptoms of overt biotin deficiency include hair loss and a scaly red rash around the eyes, nose, mouth, and genital area. Neurologic symptoms in adults have included depression, lethargy, hallucination, and numbness and tingling of the extremities. The characteristic facial rash, together with an unusual facial fat distribution, have been termed the “biotin deficient face” by some experts. Individuals with hereditary disorders of biotin metabolism resulting in functional biotin deficiency have evidence of impaired immune system function, including increased susceptibility to bacterial and fungal infections.
- Food and Nutrition Board, Institute of Medicine. Biotin. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B-6, Vitamin B-12, Pantothenic Acid, Biotin, and Choline. Washington, D.C.: NationalAcademy Press; 1998:374-389. (National Academy Press).
- Mock DM. Biotin. In: Ziegler EE, Filer LJ, eds. Present Knowledge in Nutrition. 7th ed. WashingtonD.C.: ILSI Press; 1996:220-236.
- Chapman-Smith A, Cronan JE, Jr. Molecular biology of biotin attachment to proteins. J Nutr. 1999;129(2S Suppl):477S-484S. (PubMed).
- Zempleni J, Mock DM. Biotin biochemistry and human requirements. 1999; volume 10: pages 128-138. J Nutr. Biochem. 1999;10:128-138.
- Hymes J, Wolf B. Human biotinidase isn’t just for recycling biotin. J Nutr. 1999;129(2S Suppl):485S-489S. (PubMed).
- Zempleni J, Mock DM. Marginal biotin deficiency is teratogenic. ProcSocExpBiol Med. 2000;223(1):14-21. (PubMed).
- Mock DM. Biotin. In: Shils M, Olson JA, Shike M, Ross AC, eds. Nutrition in Health and Disease. 9th ed. Baltimore: Williams & Wilkins; 1999:459-466.
- Baumgartner ER, Suormala T. Inherited defects of biotin metabolism. Biofactors. 1999;10(2-3):287-290.