Is it possible to use Strep-tag® II with streptavidin or Strep-tag® I with Strep-Tactin®?
We highly recommend using the Strep-tag II:Strep-Tactin system, which offers the optimal affinity for purification purposes (sufficient binding and optimal reversibility for mild elution). KD (Strep-tag I:streptavidin) = 36 µM KD (Strep-tag II:streptavidin) = 72 µM KD (Strep-tag I:Strep-Tactin) = 10 µM (estimated) KD (Strep-tag II:Strep-Tactin) = 1 µM Please notice that absolute binding affinity values are strongly dependent on the way of being measured and should not be compared to values determined in different assays. E.g. the KD of the Strep-tag I:streptavidin interaction has been formerly determined to be 0.7 µM (being by a factor of 50 higher than determined with the assay used above (36 µM)) via a titration colorimetry measurement. • Does the tag bind avidin? No. Therefore, avidin can be used in detection assays in order to mask naturally occurring biotinylated proteins which would generate background signals if present in the probe. For blocking biotinylated proteins in Western
