Biochemistry of Biotin

1. BIOTIN
Dr. P. SHANTHI DCP

2. Sources of Biotin
Normal bacterial flora of the gut
Distributed ubiquitously in plant and animal tissues.
Rich sources - Liver, yeast, peanut, soybean, milk and egg
yolk.

3. Structure of Biotin
Imidazole ring fused with a Thiophene
ring with a valeric acid side chain.
The carboxyl group forms an amide linkage
with the epsilon nitrogen of a lysine residue
in the apo-enzyme.

4. Biotin as Co-enzyme in Carboxylation
Reactions
• Biotin captures CO2 in its
nitrogen
• The energy is provided by
ATP.
• Then the activated carboxyl
group is transferred to the
substrate.

5. Biotin Requiring CO2 Fixation Reactions
• Acetyl CoA carboxylase - Rate limiting reaction in
biosynthesis of fatty acids
• Propionyl coA carboxylase
• Pyruvate carboxylase - TCA cycle & Gluconeogenesis

6. Biotin-Independent Carboxylation Reactions
• Carbamoyl Phosphate Synthetase - Stepping stone for UREA
and PYRIMIDINE synthesis.
• Addition of CO2 to form C6 in PURINE ring.
• Malic enzyme converting pyruvate to malate.

7. Biotin - Antagonists
• Avidin, a protein in egg white has great affinity to biotin. Avidin
is heat labile, and boiling of egg will neutralize the inhibitory
activity. One molecule of avidin can combine with four
molecules of biotin.
• Hence intake of raw (unboiled) egg may cause biotin deficiency.
• Biotin was originally named as anti-egg-whiteinjury- factor.
• Interesting fact - Egg white contains avidin and egg yolk
contains biotin.

8. Medical Applications
• The affinity of avidin to biotin is greater than most of the usual
antigen-antibody reactions.
• Therefore avidin-biotin system is commonly utilized for detection of
pathogens in the ELISA test.
• DNA is generally labelled by radioactive nucleotides.
• Recently, biotin labelling of DNA is becoming more popular. Biotin is
added to nucleotides, which will be incorporated into the newly
synthesized DNA. The fixed biotin can be identified by reaction with
avidin.
• Streptavidin purified from Streptomyces avidinii, can bind 4
molecules of biotin.

9. Medical Applications contd…..
Multiple carboxylase deficiency
• Defect in the ability to link biotin to carboxylases or
• To remove it from carboxylases during their degradation
• Treatment is biotin supplementation.

10. Deficiency of Biotin
• Prolonged use of antibacterial drugs
• Biotin deficiency symptoms include dermatitis, atrophic
glossitis, hyperesthesia, muscle pain, anorexia and
hallucinations.
• Injection of biotin 100-300 mg will bring about rapid cure of
these symptoms.
• Daily requirement ~ 200-300mg

11. THANK YOU