Avidin is a tetrameric or dimeric biotin-binding protein produced in the oviducts of birds, reptiles and amphibians and deposited in the whites of their eggs.
It consists of four high affinity binding sites for biotin. ExtrAvidin®
is prepared from egg white avidin. It is a modified form of affinity purified avidin and binds biotin with high specific activity of avidin with the low background staining of streptavidin, a biotin binding protein produced by the bacteria Streptomyces avidinii
is covalently conjugated to Cy3 dye and is used for various techniques.