Buffers & Reagents

Buffer W: Strep-Tactin®/Strep-Tactin®XT Wash Buffer

For removal of unbound proteins and other material during Strep-tag® protein purification via Strep-Tactin® and Strep-Tactin®XT columns.

Buffer BXT: Strep-Tactin®XT Elution Buffer with Biotin
Biotin displaces Strep-tag®II and Twin-Strep-tag® fusion proteins at the biotin-binding site of Strep-Tactin®XT in a competitive manner resulting in a mild elution of the protein. For your convenience, we offer biotin ready-to-use in solution (Buffer BXT with 50 mM BIotin). If you wish to prepare your own elution buffer, biotin is also offered as a lyophilized powder. Please note that after elution with Buffer BXT, the Strep-Tactin®XT column can be regenerated for atleast 3-5 times with freshly prepared NaOH (10-50 mM).

Do not use in combination with Strep-Tactin®!!!

BioLock - Biotin Blocking Solution

Biotin is often present in cell culture media. Its nearly irreversible binding to Strep-Tactin® has to be taken into account when recombinant proteins, secreted to the cell culture supernatant, are aimed to be directly purified via Strep-Tactin® affinity chromatography for two reasons:

  • It efficiently competes with the (Twin-)Strep-tag® target protein, thereby preventing it from binding to the resin
  • it inactivates Strep-Tactin® resins and thus, makes re-use impossible.

BioLock is a ready-to-use and cost effective solution for the removal of free biotin from cell culture supernatant. It simply has to be added to the cell culture supernatant prior to purification.

The required amount of BioLock for effective biotin blocking can easily be determined since 1ml BioLock blocks 70 μg biotin. In addition we provide a table with the required BioLock amounts for standard mammalian and insect cell culture media at
www.iba-lifesciences.com/technical-support.html >> troubleshooting>> Biotin Blocking


Is used for induction of tet promoter controlled pASK-IBA vectors. The E. coli expression cassette of the Strep-tag®/Strep-Tactin® overexpression system is under transcriptional control of the tetA promoter/operator and repressor. The promoter is induced by a low concentration of anhydrotetracycline (AHT) saving costs and minimizing the antibacterial influence of AHT.


Prevents biotin and biotinylated proteins from binding to Strep-Tactin® columns during Strep-tag® protein purification. This is important if growth media containing free Biotin are used (for further information see “Biotin Blocking”).

Biotin Blocking Buffer (Western blots)

For blocking biotinylated proteins in Western blots (like BCCP protein from E. coli, see Applications), the membrane is incubated with Biotin Blocking Buffer. Use a dilution of 1:1000 in standard Western blot blocking reagent prior to detecting Strep-tag® proteins with Strep-Tactin® conjugates.

Strep-tag®II Peptide

For specific customer purposes.