Biochemistry: The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Coenzymes are specialized natural reagents
Bound biotin acting as a prosthetic group
Avidin

The presence of the glycoprotein avidin in egg white remains a biochemical enigma [16]. Avidin is a tetramer with a Molecular Weight of 68,000. Each subunit of this tetramer contains a specific biotin-binding site. Avidin binds biotin with exceptional affinity: Kt ≈ 1015 M. While the evolutionary purpose of incorporating this unusual glycoprotein into egg white is unknown, avidin serves as an invaluable tool for enzymologists investigating biotin-dependent Enzymes. The addition of avidin invariably leads to the inhibition of these enzymes, and such avidin-mediated inhibition serves as a diagnostic indicator for the presence of a biotin-containing protein. Furthermore, the fact that avidin is specifically synthesized in the oviduct of the hen makes its production of considerable interest to endocrinologists, as the synthesis of this protein is regulated by the Hormones estrogen and progesterone.

Historically, avidin played a pivotal role in the discovery of biotin. The interaction between avidin and biotin is so robust that the inclusion of raw egg white in the diet of experimental animals induces severe biotin deficiency. Preventing the metabolic disruption caused by egg white served as one of the earliest bioassays for detecting biotin in natural sources.



Last update: 06/08/2026

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