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 combines high specific activity of avidin with the low background staining of streptavidin. It is a biotin binding protein produced by the bacteria Streptomyces avidinii. ExtrAvidin has been conjugated to fluorescein isothiocyanate (FITC) and is used for various techniques.
ExtrAvidin? is prepared from egg white avidin. It is a tetrameric protein containing four high affinity binding sites for biotin. It combines the high specific activity of avidin with the low background staining of streptavidin, a biotin binding protein produced by the bacteria Streptomyces avidinii. It binds biotin with the high affinity of egg white avidin, however, it does not exhibit the unwanted non-specific binding reported for egg white avidin at physiological pH, such as the staining of mast cells.
