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Avidin

Prevents biotinylated proteins from unspecific binding to Strep-Tactin columns during Strep-tag protein purification.

D-Biotin (not suitable for standard Strep-tag applications)

D-Biotin should be used for elution of Strep-tag/OneSTrEP-tag fusion proteins in certain applications only. It is recommended for elution from Strep-Tactin Spin columns and MagStrep beads because of the higher affinity to Strep-Tactin which allows a more efficient elution (compared to Desthiobiotin) of (One)Strep-tag fusion proteins. For protein complex and PPI applications Biotin is also recommended for elution since the Strep-Tactin resins should not be regenerated to avoid isolation of cross contaminations.

Please note that after elution with Biotin the Strep-Tactin resin cannot be regenerated!

Streptavidin, lyophilized (not suitable for Strep-tag^® applications):

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.

Avidin Specifications

Description	Avidin is a tetrameric biotin binding protein (KD for biotin > 10-14) from egg white which does not bind to the Strep-tag.
Form	white powder
Activity	binding of >45 nmol biotin/mg avidin (determined by HABA dye binding method)
Stability	12 months after shipping
Storage	-20°C, solutions in dilute buffers are stable at +4°C
Shipment	RT

D-Biotin Specifications

Description	Vitamin H; (+)-Biotin
Form	white powder
FW	244.3, C10H₁₆N₂O₃S
Stability	12 months after shipping

Storage	2 - 8 °C
Shipment	RT

Please note that after elution with Biotin the Strep-Tactin resin cannot be regenerated!

Streptavidin Specifications

Form	Lyophilized in 10 mM potassium phosphate buffer pH 6.5
MW per tetramer	~53 000
Extinction coefficient per subunit	ε₂₈₀ = 41326 M^-1cm^-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

Quality control by SDS-PAGE:

P1 = 50 µg Streptavidin, boiled
M = marker (~ 0.5 µg per band)