Biotin was once known as coenzyme R and vitamin H. Biotin is water-soluble, which means that the body does not store it. It has many important functions in the body. It is required for the function of a variety of enzymes, called carboxylases. These biotin-containing enzymes are involved in important metabolic pathways, such as the production of glucose and fatty acids. Streptavidin is a 52.8 kDa protein purified from Streptomyces avedini. Streptavidin homotetramers have an extremely high affinity for biotin. The binding of biotin to streptavidin is one of the strongest non-covalent interactions known in nature, with a dissociation constant of approximately 1 μmol/L. Streptavidin is widely used in molecular biology and bionanotechnology due to the resistance of the streptavidin-biotin complex to organic solvents, denaturants, detergents, proteolytic enzymes, and extremes of temperature and pH.