A tetrameric biotin-binding protein capable of binding four molecules of biotin per molecule. Streptavidin may be labeled with a fluorophore, an enzyme, or gold particle to facilitate detection.

The binding partner to biotin (see biotin).

A small bacterial protein that binds with high affinity to the vitamin biotin. This streptavidin-biotin combination can be used to link molecules such as radioisotopes and monoclonal antibodies together. These bound products have the property of being attracted to, and attached to, cancer cells, rather than normal cells. The radiolabeled products are more easily removed from the body thus decreasing their toxicity.