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The role of Biotin in metabolism and

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Biotin, a water-soluble vitamin, is used as an essential coenzyme
for five carboxylases in mammals; propionyl-CoA carboxylase;
methylcrotonyl-CoA carboxylase; pyruvate carboxylase, and two
isoforms of acetyl-CoA carboxylase. Each of these biotin-
dependent carboxylases catalyzes an essential step in pathways
involved in gluconeogenesis, fatty acid metabolism, and amino
acid catabolism; thus, biotin plays an essential role in maintaining
metabolic homeostasis.
Carboxylase activities decrease substantially in response to biotin
deficiency. Biotin has been associated with several metabolic
diseases in humans and some are related to enzyme deficiencies
involved in biotin metabolism. Biotin deficiency may be caused by
insufficient dietary uptake of biotin, drugvitamin interactions
and, by increased biotin catabolism during pregnancy and in
smokers. Symptoms of biotin deficiency include seizures,
hypotonia, ataxia, dermatitis, hair loss, mental retardation,
ketolactic acidosis, organic aciduria and fetal malformations.
However, not all biotin-responsive disorders can be explained
based on the classical role of biotin in cell metabolism. More
recently, scientist suggest that biotin may be involved in
regulating transcription or protein expression of different
proteins. Biotinylation of histones and triggering of transduction
signaling cascades have been suggested as underlying
mechanisms behind these non classical biotin deficient
manifestation in humans.

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Biotin, a water-soluble vitamin belonging to the B complex, serves
two different functions in a cell. First act as a coenzyme in each of
five dependent carboxylases in humans; acetyl-CoA carboxylases
(ACC)a and (ACC)β, propionyl-CoA carboxylase (PCC), 3-
methylcrotonyl-CoA carboxylase (MCC) and pyruvate carboxylase
(PC) (Camporeale and Zempleni., 2006). Each of these biotin-
dependent carboxylases catalyzes an essential step in pathways
involved in fatty acid biosynthesis, gluconeogenesis and
tricarboxylic acid cycle anaplerosis. Therefore, biotin homeostasis
is crucial for maintaining normal body functions, in particular, in
the heart muscle and brain (Ozand et al., 1998). Biotin
homeostasis is maintained by dietary intake, the biotin
transporters monocarboxylate transporter 1 (MCT1) and sodium-
dependent multivitamin transporter (SMVT), the biotin protein
ligase holocarboxylase synthetase (HCS) and the biotin peptidyl
hydrolase biotinidase (BTD) (Zempleni et al., 2008).
Second, scientist suggest that biotin may play a role in other
cellular events such as transcriptional or translational regulation
or activity enhancement of different hepatic enzymes that include
glucokinase, phosphoenol pyruvate carboxykinase, and most of
the proteins involved in biotin metabolism (Pacheco-Alvarez D et
al., 2005).
In addition, biotin deficiency has shown to be teratogenic in
several animals and perhaps in humans, and the cause of several
neurologic diseases (Mock et al.,2003). The exact mechanisms
involved in these other functions of biotin are still unknown;
however, it is possible that biotin may have been selected during
evolution to play different roles in metabolism and gene

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