Streptavidin is a 22- 55 kDa (subunit MW 14 kDa) biotin-binding protein isolated from Streptomyces avidini. Streptavidin is superior to avidin, because it does not contain carbohydrate like avidin and has no net charge at neutral pH. Streptavidin~biotin system is routinely used in Immunohistochemistry (IHC). Extinction Coefficient 1% A280=32.0. Protein content: > 95%; Peroxidase used for conjugation is 44 kDa glycoprotein isolated from horseradish roots. The Rz (Reinhetszahl), absorbance ratio of A403/A275 is ~3.0. One mg of Streptavidin is conjugated with peroxidase, in equimolar ratio. Unconjugated Streptavidin is removed.