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Avidin and Streptavidin Reagents

Avidin is a tetrameric protein commonly isolated from egg whites. Avidin binds to biotin with strength approaching that of a covalent bond. Disruption of the avidin-biotin bond occurs only under extraordinary conditions, such as pH 1.5 with 6 M guanidium hydrocholoride. Fluorescent avidin can bind to biotinylated antibodies used in immunohistochemistry and immunocytochemistry. Avidin thiol can bind to gold surfaces and act as a glue for biotinylated proteins. Avidin agarose is useful for efficient removal of biotinylated proteins from a liquid phase.

Streptavidin is similar to avidin in that it binds biotin and exists as a tetramer. Streptavidin’s primary advantage is that it less charged under neutral conditions and is therefore less likely to be involved in unwanted ionic interactions.