Introduction  Streptavidin is a tetrameric protein secreted by Streptomyces avidinii which binds firmly to biotin. Streptavidin is wilyde used in molecular biology through its unique high affinity for the vitamin biotin. The dissociation constant (Kd) of the biotin-streptavidin complex is about ~10-15 mol/L. The strong affinity recognition of biotin and biotinylated molecules has made streptavidin one of the most important components in diagnostics and laboratory kits. The streptavidin/biotin system has one of the biggest free energies of association of yet observed for noncovalent binding of a protein and small ligand in aqueous solution (K_assoc = 10**14). The complexes are also extremely stable over a wide range of temperature and pH. 

Description  The Streptavidin preparation contains an N- and C-terminal shortened variant (core streptavidin) with improved properties concerning homogeneity, solubility, resistance towards proteolytic degradation and accessibility of the biotin binding pocket as compared to native streptavidin. Streptavidin has a molecular weight of 55kDa. 

Source  Bacterium Streptomyces avidinii. 

Physical Appearance Sterile Filtered lyophilized powder. 

Formulation  Lyophilized (1mg/ml) in 50mM NaCl, pH 9.0.

Solubility  Gives a clear solution at 5mg/ml in 0.1M NaCl. 

Stability  Streptavidin although stable at 4°C for 3 weeks, should be stored desiccated below -18°C.

For longer storage in dissolved form add 1mM EDTA and/or 0.02 % NaN3 or pass the solution through a sterile filter.

Please prevent freeze-thaw cycles. 

Application  Streptavidin may be used to visualize biotin conjugated molecules in ELISA, blotting and histological technique. 

Specific Activity  Greater than 15.7 U/mg, 1 unit binds 1µg biotin. 

Proteolytic Activity Less than 10-3 U/mg protein (Azocoll, 25°C, 24 h, pH 8.0). 

Purity  Greater than 95.0% as determined by SDS-PAGE.