Avidin
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Avidin is a toxic protein found in egg white that binds with biotin, found in egg yolk. In biochemical applications, streptavidin, which binds very tightly to Biotin, is often used in place of avidin.
[edit] Relationship between avidin and biotin
Avidin is a glycoprotein that has a very strong affinity for biotin with a kD (dissociation constant) approximate to 10-15 M-1, the highest known between any ligand and a protein, and, as such, prevents biotin absorption in the gastrointestinal tract. Avidin is a tetrameric protein attaching four molecules of biotin per tetramer.
Avidin-induced biotin-deficient meals, especially those rich in raw egg white, make it impossible for biotin to be absorbed in the small intestine. Through the use of an enzyme, lyzine hydroxylase, and the intraveinous administration of avidinbiotin, complex biotin can be released into the system. Basically, Avidin is too large to be absorbed into the intestines, and by bonding tightly to Biotin, it makes the protein molecules of Biotin too large to pass into the intestine and get absorbed.
Avidin's affinity for biotin is exploited in both ELISPOT and ELISA assays.
[edit] References
- ↑ Bayer, Ed: "The Avidin-Biotin Complex", Dept. of Biological Chemistry, Weizmann Institute of Science, Israel
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