Biotin (Vitamin B7) Flashcards
What is the structure of biotin?
Imidazole ring fused to a thiophene ring with a valeric acid side chain
COOH binds to the ε-NH2 group of lysine of the enzyme to function as a coenzyme (Biotinyllysine)
What is the role of biotin coenzymes in metabolism?
Function as coenzymes in carboxylation reactions
1. Pyruvate carboxylase: Involved in glucogenesis (First reaction in pathway that converts 3-carbon precursors to glucose and also replenishes oxaloacetate for citric acid cycle)
2. Acetyl-CoA carboxylase: Biosynthesis of fatty acids (Commits acetyl units to fatty acid synthesis by forming malonyl-CoA)
3. Branched-chain amino acid metabolism
Additional functions listed in the table
RDA of biotin
30-100 µg/day
What are the sources of biotin?
Liver, egg yolk, cereals, peanuts and yeast
Also produced by gastrointestinal bacteria
What are the symptoms of biotin deficiency?
Anemia
Dermatitis
Hair loss
Muscle pain
Hallucinations
Hyperesthesia
Depression
How may deficiency of biotin occur?
Consumption of avidin protein in egg whites which bind to biotin very tightly (very high consumption of required)
Breast fed infants with persistent diarrhea
Long term antiobiotic therapy
Marginal deficiency can also be seen in alcoholics, pregnancy and lactation
What is avidin?
Antagonist of biotin
What are the characteristics of avidin?
Heat labile
1 molecule of avidin combines with 4 molecules of biotin
Affinity of avidin to biotin is greater than most antigen-antibody reactions. It is one of the strongest known protein-ligand interactions
This system is used for detection of pathogens in ELISA test and is often used in different biotechnological applications
Why is deficiency of biotin rare?
GI bacteria produce biotin in excess of daily requirement
Widespread food sources make avoidance of biotin consumption difficult
