Avidin is a glycoprotein present in egg albumen. The concentration varies with hen's age, but the mean is 0.05% of the total egg albumen protein (75). The protein is 66,000 to 69,000 Da and has four identical subunits of 128 amino acids each. Avidin strongly binds the cofactor biotin at a ratio of four molecules of biotin per molecule of avidin. Biotin is a cofactor for enzymes in the tricarboxylic acid cycle and fatty acid biosynthesis. Avidin inhibits growth of some bacteria and yeasts that have a requirement for biotin with the primary mechanism being nutrient deprivation.
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