Vitamin B7

Question 1

Vitamin B7, biotin, is a vitamin required in the human diet; it is abundant in many foods and is synthesized by intestinal bacteria. Lysine residue reacts with biotin through an amide linkage to form _____________, which is the active form of the vitamin.

Answer 1

biocytin

Question 2

State the roles of vitamin B7

Answer 2

• Biocytin is an enzymatic cofactor involved in carboxylation reactions e.g. pyruvate carboxylase reaction: Pyruvate + HCO3- + ATP –> oxaloacetate + ADP + P
• The carboxylation reaction involves biotin as a carrier of activated bicarbonate. Biotin plays a key role in many carboxylation reactions.
• It is a specialized carrier of one-carbon groups in their most oxidized form: CO2

Question 3

Deficiency of biotin?

Answer 3

Biotindeficiencyisrare,butcansometimesbecausedbya diet rich in raw eggs. Egg whites contain a Iarge amount of the protein avidin, which binds very tightly to biotin and prevents its absorption in the intestine.