Avidin Reagents

Avidin is a 65 kDa protein found in egg whites. It consists of 4 identical subunits, each with a high-affinity binding site for biotin (Vitamin H). The strength of the binding (Ka = 1015) results in an essentially irreversible interaction. This interaction has been exploited for immunolabeling of antigens in histochemical, blotting, and multiwell assays. Biotinylated probes, which may be secondary antibodies, lectins, or other bioactive compounds, bind to targets on tissue samples, microtiter plates, or membranes. Avidin conjugated to enzymes, fluorochromes, or other labels binds to the biotinylated probes for visualization, either by detection of fluorescence or enzymatic conversion of substrate to produce a visible end product. In this system avidin serves as a secondary probe, attaching to the primary biotinylated probe at several sites and amplifying the signal. Use of an avidin-enzyme conjugate provides further amplification by conversion of substrate by the enzyme, which will continue to produce a visible product until the substrate is exhausted or the reaction is stopped.

Avidin has been reported to exhibit non-specific binding to membranes and tissues. For applications where nonspecific binding of avidin is a problem, Sigma offers Streptavidin and ExtrAvidin®.

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A9275 Avidin from egg white BioUltra, lyophilized powder, ≥10 units/mg protein (E1%/280), ≥98% (SDS-PAGE)
A9207 Avidin−Agarose from egg white aqueous glycerol suspension
A7294 Avidin–Alkaline Phosphatase buffered aqueous solution
A5405 Avidin-ferritin labeled avidin from egg white, lyophilized powder
A2901 Avidin–FITC from egg white lyophilized powder
A2050 Avidin–FITC from egg white buffered aqueous solution
A3151 Avidin–Peroxidase lyophilized powder
A7419 Avidin–Peroxidase buffered aqueous solution
A2348 Avidin−Sulforhodamine 101 lyophilized powder
H2153 HABA/Avidin Reagent lyophilized powder
A3907 Succinyl-Avidin