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biotin deficiency
Biotin deficiency is a rare nutritional disorder which can become serious, even fatal, if allowed to progress untreated. It can occur in people of any age, ancestry, or gender. Biotin is part of the B vitamin family.
Biotin deficiency rarely occurs among healthy people because the daily requirement of biotin is low, many foods provide adequate amounts of it, intestinal bacteria synthesize small amounts of it, and the body effectively scavenges and recycles it from bodily waste. However, deficiencies can be caused by consuming raw egg whites over a period of months to years. Egg whites contain high levels of avidin, a protein that binds biotin strongly. When cooked, avidin is partially denatured and binding to biotin is reduced. However one study showed that 30-40% of the avidin activity was still present in the white after frying or boiling.〔http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1991.tb05361.x/abstract〕 Hence excessive cooked egg white consumption could possibly cause biotin deficiency. Genetic disorders such as Biotinidase deficiency, Multiple carboxylase deficiency, and Holocarboxylase synthetase deficiency can also lead to inborn or late-onset forms of biotin deficiency. In all cases – dietary, genetic, or otherwise – supplementation with biotin is the primary method of treatment.
== Biochemistry ==
Biotin is a coenzyme for five carboxylases in the human body (propionyl-CoA carboxylase, methylcrotonyl-CoA carboxylase, pyruvate carboxylase, and 2 forms of acetyl-CoA carboxylase.) Therefore, biotin is essential for amino acid catabolism, gluconeogenesis, and fatty acid metabolism.〔Greenway et al. 2011, p. 178.〕 Biotin is also necessary for gene stability because it is covalently attached to histones. Biotinylated histones play a role in repression of transposable elements and some genes.〔Zempleni et al. 2008, p. 715.〕 Normally, the amount of biotin in the body is regulated by dietary intake, biotin transporters (monocarboxylate transporter 1 and sodium-dependent multivitamin transporter), peptidyl hydrolase biotinidase (BTD), and the protein ligase holocarboxylase synthetase. When any of these regulatory factors are inhibited, biotin deficiency could occur.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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