Streptavidin

Purified from the bacterium Streptomyces avidinii, this 60 kDa homotetrameric biotin-binding protein is supplied by Antibodies.com as a 5 mg lyophilized powder for use as an assistive reagent in detection workflows. Each subunit contributes one biotin-binding pocket, giving four binding sites per molecule and a combined dissociation constant near 10^-14 M for biotin, one of the strongest known non-covalent biological interactions.

The lyophilized format allows long-term storage with minimal activity loss and rapid reconstitution in water or working buffer before use. In Western blot and other immunoassay workflows, streptavidin amplifies signal by recruiting additional reporter molecules per bound biotin, increasing sensitivity over direct antibody detection. The protein is also widely used as a bridging reagent in pull-down assays, immunohistochemistry, and flow cytometry.

Because the molecule is non-glycosylated and carries a near-neutral isoelectric point (~5 to 6), non-specific binding to mammalian tissues and nitrocellulose membranes is reduced compared with egg-white avidin. For the 5 mg pack size, typical working concentrations fall in the 1 to 5 µg/mL range depending on the chosen detection chemistry. Researchers should aliquot immediately after reconstitution, refrigerate for short-term use, and freeze at -20 °C for longer-term storage to preserve binding activity.