Avidin is a basic glycoprotein consisting of four essentially identical subunits. The combined molecular weight of the subunits is about 66,000. Each subunit is a single polypeptide chain containing 128 amino acid residues with alanine at the N-terminal, glutamic acid at the C-terminal, and a carbohydrate moiety attached at the aspariginyl residue, position 17. It is isolated from raw egg white. It exhibits high binding affinity for biotin and is capable of producing biotin deficiency in rats and chicks. It also occurs in the white portion of eggs and the oviducts of birds and amphibia. It is destroyed by cooking or irradiation.

• Soluble in water or dilute aqueous buffer
• Specific activity: 10-15 units/mg protein
• Isoelectric point (pI): 10 (Lit.)

Avidin was used in an assay using functionalised xenon as a biosensor to detect biotin-avidin binding.

Unit definition: One unit will bind 1 µg of D-biotin at pH 8,9.