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Biotin and Avidin/Streptavidin Reagents

When we introduced the Biotin-Avidin (now also Streptavidin) System a substantial amplification over the earlier methods was achieved. Avidin is an egg-white derived glycoprotein with an extraordinarily high affinity (affinity constant > 1015 M-1) for biotin. Streptavidin is similar in properties to avidin but has a lower affinity for biotin. Many biotin molecules can be coupled to a protein, enabling the biotinylated protein to bind more than one molecule of avidin. If biotinylation is performed under gentle conditions, the biological activity of the protein can be preserved. By covalently linking avidin or streptavidin with different ligands such as fluorochromes, enzymes or EM markers, what we have termed the Biotin-Avidin System (or Biotin-Streptavidin System) can be utilized to study a wide variety of biological structures and processes. The Biotin-Avidin/Streptavidin System has proven to be particularly useful in the detection and localization of antigens, glycoconjugates, and nucleic acids by employing biotinylated antibodies, lectins, or nucleic acid probes.