Biotin is a cofactor for carboxylase enzymes. A patient on long-term raw egg white diet develops biotin deficiency because:
- A Avidin sequesters biotin in the intestinal lumen with very high affinity (Kd ~10-15 M), preventing luminal biotin from being absorbed ✓
- B Avidin in raw egg white irreversibly binds biotin in the intestinal lumen, preventing absorption
- C Raw egg white contains a biotin-destroying protease (biotinidase) that cleaves dietary biotin
- D Egg white protein competes with biotin for the multivitamin transporter SMVT in intestinal enterocytes
Explanation
Avidin, a glycoprotein in raw egg white, binds biotin with extraordinary affinity (Kd ~10-15 M, one of the strongest non-covalent interactions known). Avidin-biotin binding in the intestinal lumen sequesters dietary and microbially-synthesized biotin, preventing its absorption by the sodium-dependent multivitamin transporter (SMVT/SLC5A6). Cooking denatures avidin, eliminating this effect. Biotin deficiency causes dermatitis, alopecia, neurological symptoms, and impairs all four biotin-dependent carboxylases: acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and 3-methylcrotonyl-CoA carboxylase.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.