Streptavidin is a tetrameric protein composed of identic subunits. Each subunit binds one biotin molecule with a KD of ~1x10-15 M. The 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.
Form Lyophilized in 10 mM potassium phosphate buffer pH 6.5
MW per tetramer ~53 000
Extinction coefficient per subunit ε280 = 41326 M-1 cm-1
Specific activity > 17 U/mg (one unit binds 1 µg D-biotin)
Purity > 95 % as estimated by SDS-PAGE
Proteolytic activity < 10-3 U/mg protein (Azocoll, 25 °C, 24 h, pH 8.0)
Reconstitution Dissolve with water 
Storage (lyophilized) -20 °C
Stability (lyophilized) 2 years after shipping
Storage (dissolved) 4 °C; for longer storage in dissolved form add 1 mM EDTA and/or 0.02 % NaN3 or pass the solution through a sterile filter
Shipment Room temperature