Biotin, a member of the B Vitamin family, is an essential nutrient in human nutrition
It is involved in the biosynthesis of fatty acids, gluconeogenesis, energy production, the metabolism of the branched-chain amino acids (L-leucine, L-isoleucine, L-valine) and the de novo synthesis of purine nucleotides. Recent research indicates that biotin plays a role in gene expression, both at the transcriptional and translational levels, and that it may also play a role in DNA replication.
The first demonstration of biotin-deficiency in animals was observed in animals fed raw egg white. Rats fed egg white protein were found to develop dermatitis, hair loss and neuromuscular dysfunction. This syndrome was called egg white injury and was discovered to be caused by a glycoprotein found in egg white called avidin. It was subsequently found that egg white injury could be cured by a liver factor which was first called protective factor X and later determined to be biotin. Because biotin cured the skin disorder of egg white injury it was called vitamin H. H is for haut, the German word for skin. Avidin causes egg white injury because it binds very tightly to biotin, preventing its absorption. This is only true for native avidin, which is resistant to hydrolysis by proteolytic enzymes. When egg white is cooked, avidin is denatured and denatured avidin is digested by proteolytic enzymes.
Here is the biochemical pathways for biotin for those who desire a little more in-depth study. Biotin is the coenzyme for four carboxylases. Acetyl coenzyme A (CoA) carboxylase, found in both the mitochondria and cytosol, catalyzes the carboxylation of acetyl-CoA to malonyl-CoA. Malonyl-CoA is the immediate precursor of 14 of the 16 carbon atoms of the fatty acid palmitic acid. It is also the immediate precursor of all of the fatty acids up to palmitic acid. Further, the reaction catalyzed by acetyl-CoA carboxylase, a complex reaction, is the primary regulatory, or rate-limiting, step in the biosynthesis of fatty acids. Pyruvate carboxylase, which is located in the mitochondria, catalyzes the carboxylation of pyruvate to form oxaloacetate. Oxaloacetate can be metabolized in the tricarboxylic acid cycle or it can be converted to glucose in the liver and kidney and other tissues that are involved in gluconeogenesis. The formation of oxaloacetate from pyruvate is known as an anaplerotic reaction. Anaplerotic is from the Greek word anaplerosis, meaning filling up or restoration. The pyruvate carboxylate reaction is the principal reaction which replenishes tricarboxylic acid cycle intermediates. Methylcrotonyl-CoA carboxylase, also located in the mitochondria, is involved in the metabolism of L-leucine, while the mitochondrial enzyme propionyl-CoA carboxylase is involved in the metabolism of L-isoleucine and L-valine, as well as L-threonine and L¬methionine.
Biotin has been found to inhibit the generation of reactive oxygen species, including superoxide anions, by neutrophils.
The symptoms and signs of biotin-deficiency, include a generalized erythematous scaly skin eruption, alopecia, conjunctivitis and neurological abnormalities. The rash may be distributed around the eyes, nose, mouth, ears and perineal orifices. The facial appearance associated with the deficiency, with the rash around the eyes, nose and mouth along with an unusual distribution of facial fat, is called biotin deficiency facies. In biotin deficient infants, the neurological findings are hypotonia, lethargy and developmental delay. In adults, the neurological findings are lethargy, depression, hallucinations and paresthesias of the extremities. Marginal biotin status may occur under certain conditions, e.g., during the first trimester of pregnancy, and it is thought that this situation may be teratogenic. Functional biotin deficiency occurs in certain genetic disorders.