Vitamin B7 (Biotin)

Summary

Vitamin B7 (Biotin) is a water-soluble vitamin, important in metabolism as a cofactor for several important carboxylase enzymes. Enzymes dependent on biotin include pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase.

Biotin deficiency is rare, but it can be induced by antibiotic usage or excessive consumption of raw egg whites. In particular, the avidin in egg whites binds and sequesters biotin. Patients with a biotin deficiency typically present with dermatitis, diarrhea, and alopecia.

Key Points

• Biotin (Vitamin B7)
  • cofactor for carboxylation enzymes (adds 1 carbon group):
    • Pyruvate carboxylase (in Pyruvate Metabolism)
      • Pyruvate (3C) → oxaloacetate (4C)
        • first committed step of gluconeogenesis
    • Acetyl-CoA carboxylase (in Fatty Acid Synthesis)
      • Acetyl-CoA (2C) → Malonyl CoA (3C)
    • Propionyl-CoA carboxylase (in Propionic Acid Pathway)
      • Propionyl-CoA (3C) → methylmalonyl-CoA (4C)
        • Important in metabolism of isoleucine, valine, threonine, methionine, and odd-chain FAs
• Biotin (Vitamin B7) Deficiency
  • relatively rare, seen with:
    • excessive consumption of raw egg whites
      • avidin in egg whites binds biotin, impairing GI absorption
    • broad-spectrum antibiotic use
      • kills biotin-producing bacteria in GI tract
  • symptoms include dermatitis, enteritis, and alopecia

Find Vitamin B7 and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.