Streptavidin is a biotin-binding protein found in the culture broth of the bacterium Streptomyces avidinii. Streptavidin binds 4 moles of biotin per mole of protein with an extremely high affinity. Streptavidin lacks carbohydrate side chains present on avidin and has an isoelectric point of 6.5 (vs 10 for avidin) close to where most useful biological interactions occur. As a result, streptavidin frequently exhibits much lower non-specific binding thaavidin does.