Biotin, or vitamin B-7, is a member of the B-complex family. It is a water-soluble nutrient, meaning that excessive doses are easily eliminated in your urine. The Linus Pauling Institute at Oregon State University reports that biotin was not even considered to be a vitamin until 40 years after it was discovered. Its importance in human metabolism was established when biotin deficiencies developed in people who ate large amounts of raw eggs. Avidin, a protein found in raw egg whites, binds to biotin and prevents its absorption by your intestines.
Coenzyme
Biotin serves as a co-factor for a family of cellular enzymes called carboxylases. These enzymes add single-carbon groups to other molecules, such as fatty acids and amino acids, so they can be used in other processes within your body. Biotin is required to activate five separate carboxylase systems, each of which performs an essential metabolic task. If a carboxylase is not "biotinylated," it becomes inactive and cannot participate in its respective metabolic pathway.
Fatty Acid Synthesis
Fatty acids are long chains of carbon atoms that serve as important energy sources for your cells. Their production requires carboxylation of a precursor molecule called acetyl-CoA to form malonyl-CoA, which is then shunted into the fatty acid-synthesis pathway. Two distinct forms of biotinylated carboxylase enzymes -- one in the cytoplasm of your cells and one in your mitochondria -- regulate the carboxylation of acetyl-CoA and the synthesis of fatty acids containing an even number of carbon atoms. A third form of carboxylase is required for the synthesis of fatty acids containing an odd number of carbon atoms.
Amino Acid Metabolism
Amino acids are the building blocks for proteins. Like beads threaded onto a string, amino acids are sequentially joined together to form long polypeptide chains, which are then folded and modified to form proteins, enzymes, hormones and other important molecules. Amino acids also serve as precursors for neurotransmitters and as substrates for energy production. Biotinylated carboxylases are essential for preparing amino acids for use in these different metabolic pathways.
Gluconeogenesis
Gluconeogenesis, or "new glucose production," is a process your liver uses to convert noncarbohydrate molecules -- amino acids and glycerol -- into glucose, which is your body's main source of cellular fuel. A biotinylated enzyme called pyruvate decarboxylase is a key player in this critical metabolic pathway. A September 2010 review in "Molecular Genetics and Metabolism" describes three forms of hereditary pyruvate carboxylase deficiency, two of which are typically fatal during childhood.
Considerations and Recommendations
Biotin is an essential nutrient in humans, who cannot synthesize it within their own cells. However, some biotin is produced by bacteria in your intestine and subsequently absorbed into your bloodstream, so biotin deficiency is uncommon. Liver, yeast, peanuts, unpolished rice, carrots, cabbage and milk are good dietary sources of biotin. Recommended dietary allowances for biotin vary from 5 mcg for infants to 35 mcg for lactating females.
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