Strepavidin-collodial gold conjugate is a component of streptavidin/colloidal gold-biotin detection systems use in immunoblotting, light microscopy, and immunoelectron microscopy applications. It is commonly used in postembedding immunocytochemistry.
Streptavidin is a protein produced by the bacterium Streptomyces avidinii. It has four binding sites for biotin as does avidin. Both have been used extensively as probes in immunochemical systems, conjugated to antibodies, enzymes, fluorochromes and gold. Avidin is highly basic (pI ~ 10.5), compared to streptavidin (pI ~ 5-6). Avidin has a slightly higher binding capacity for biotin than streptavidin does, but it has glycosylated side chains which give higher backgrounds in blotting techniques than does streptavidin, which is not a glycoprotein. Streptavidin is more resistant than avidin to dissociation into subunits by guanidinium chloride. Streptavidin may be conjugated to colloidal gold.
