Avidin is a protein found in the eggs of birds, amphibians, and reptiles that binds easily to biotin. A biotin deficiency can cause hair loss, rash, and neurological symptoms. Cooking eggs deactivates avidin, but genetic disorders, stomach removal, and excessive alcohol consumption can increase the need for biotin. Streptavidin, a similar protein, is used in laboratory applications.
Avidin is a protein found in the eggs of birds, amphibians, and reptiles. It is produced in the oviducts of these animals. An oviduct is the route that leads from the ovaries to the outside of the body in non-mammalian vertebrates.
In eggs, avidin represents only 0.05 percent of their total protein. Avidin is tetramic, meaning it is made up of four identical subunits. The most important action of this protein is that it binds very easily to the vitamin biotin.
Biotin is a water soluble vitamin that is necessary for various bodily functions. It is required for cell growth, the production of fatty acids, and the metabolism of amino acids and fats. This vitamin also helps in the transfer of carbon dioxide and promotes the growth of hair and nails. Natural sources of this vitamin include bananas, salmon, liver, and egg yolks. Bacteria present in the human intestinal tract also produce biotin.
With the abundance of biotin sources available, combined with the fact that very little is needed by the human body to function, a deficiency in this vitamin is rare. A diet high in raw egg whites or other forms of raw eggs can lead to a deficiency of this vitamin. The avidin present in the eggs will bind any biotin present in the body, rendering it useless. When an egg is cooked, the avidin within the egg white is deactivated, but the biotin present in the egg yolk is not affected.
A biotin deficiency causes hair loss, a scaly rash around the eyes, and high blood cholesterol. It also causes neurological symptoms, such as depression, hallucinations, and numbness in the hands and feet. A biotin-deficient person is often said to have a biotin-deficient face characterized by an eye rash and an odd distribution of fat in the facial area.
There are also genetic disorders that cause an increased need for biotin, and certain procedures, such as stomach removal, can have the same effect. Excessive alcohol consumption also leads to an increased need for biotin. Pregnancy is associated with an increased need for this vitamin, but only limited research has been done to determine the reason for this need.
Another form of avidin is streptavidin. It is produced by the bacterium streptomyces avidinii, and has the same affinity for biotin as avidin. Streptavidin also has a tetramaic structure. This protein is used in laboratory applications, such as staining cells and tissues, and is also used as a biotin detector.
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