Biotin (Vitamin B7)

Biotin is a coenzyme in carboxylation reactions, in which it serves as a carrier of activated carbon dioxide (CO2) . Biotin is covalently bound to the ε-amino group of lysine residues in biotin-dependent enzymes (Fig. 1). Biotin deficiency does not occur naturally because the vitamin is widely distributed in food. Also, a large percentage of the biotin requirement in humans is supplied by intestinal bacteria. However, the addition of raw egg white to the diet as a source of protein can induce symptoms of biotin deficiency, namely, dermatitis, hair loss, loss of appetite, and nausea. Raw egg white contains the glycoprotein avidin, which tightly binds biotin and prevents its absorption from the intestine.
With a normal diet, however, it has been estimated that 20 eggs/day would be required to induce a deficiency syndrome. [Note: Inclusion of raw eggs in the diet is not recommended because of the possibility of salmonellosis caused by infection with Salmonella enterica.]

Figure 1:  A.Structure of biotin. B.Biotin covalently bound to a lysyl residue of a biotin-dependent enzyme. CO2 = carbon dioxide. Multiple carboxylase deficiency results from decreased ability to add biotin to carboxylases during their synthesis or to remove it during their degradation. Treatment is biotin supplementation.