Streptavidin is a 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%; Alkaline Phosphatase (ALP) used in this conjugation is 140 KDa enzyme purified from calf intestine.