The high affinity of the non-covalent interaction between biotin and streptavidin (Kd 4×10-14 M) forms the basis for our SAVIEW® PLUS immunostaining kits. Streptavidin is a tetrameric protein which can bind to four molecules of biotin. Streptavidin gives superior results as compared to avidin (which is used in ABC system) because its isoelectric point is closer to neutral pH, whereas avidin is positively charged at physiological pH. Moreover, streptavidin does not carry any carbohydrate side chain, whereas avidin is composed of 70% of carbohydrate. Because of these reasons, streptavidin has the advantage of much lower nonspecific binding than avidin.

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