4. • 2 rings : Imidazole ring & thiophene
derivative.
• Occurs in free form & bound form in tissues
and food.
• Exists as biocytin, oxybiotin and desthiobiotin
in bound form.
5. • Depending on the side chain :
1. Alpha-biotin
2. Beta biotin
o Covalently attached to epsilon amino group
of lysine to form biocytin (ε-N-Biotinyl lysine)
• Biocytin is present in tissues.
• Desthiobiotin and oxybiotin: These are
biologically active in certain strains of yeast
and bacteria.
6. Biosynthesis and Metabolism
• Biotin is not synthesised in humans.
• It has to be taken in the diet.
• Synthesized by bacterial flora of intestine,
fungus and yeast.
• Formed in leaf and root in plants
• Co-enzyme R is a growth essential for the
nitrogen-fixing organisms.
7. STORAGE
• Stored to a limited extent in Liver & kidneys.
SOURCES
• Widely distributed in plants & animals.
Plants : leafy vegetables & cereals.
Animals : liver, kidney, milk & egg yolk.
8. Excretion
It is excreted in urine, faeces and in milk
secretion.
Metabolic role of biotin
1. Biotin acts as coenzyme for
carboxylation reactions catalysed by
Carboxylases.
9. • Biotin is first converted to carboxy-biotin
complex by reaction with bicarbonate & ATP.
• CO2-biotin complex is the source of active
CO2 which is transferred to the substrate.
10. Examples of Carboxylation reactions :
1) Conversion of pyruvate to OAA.
Biological Significance
• It is the first reaction of gluconeogenesis.
• OAA can be used for glucose production or for the
functioning of TCA cycle depending on need of cell.
11. 2) Carboxylation of propionyl coA
Biological significance
• Succinyl CoA enters TCA cycle for complete oxidation to
provide energy.
• Propionyl CoA is glucogenic in nature.
12. 3) Conversion of Acetyl CoA to Malonyl CoA
Biological Significance
• First &rate limiting reaction of FA biosynthesis.
• In absence of biotin, FA synthesis is enormously affected.
13. 4) Carboxylation of B-methyl crotonyl CoA
Biological Significance
• Important reaction of Leucine Metabolism.
• Biotin deficiency impairs leucine metabolism greatly.
14. Role of Biotin in cell division
• Required for cell division & tissue
proliferation.
• Has an active role in maintaining texture of
skin, hair and nails. (Beauty vit)
15. Deficiency of Biotin
Very rare
Occurs except under 2 conditions:
1. Congenital deficiency
• It is due to deficiency of enzyme
holocarboxylase synthetase.
16. Deficiency of the HCS enzyme makes the
carboxylases inefficient, precipitating all the
manifestations of biotin deficiency.
Also, CO2 transfer reactions are grossly
affected.
Clinical Manifestations
• Growth retardation
• Dermatitis
• Loss of hair
• Greying of hair
• Abdominal discomfort and diarrhea
18. Treatment :
No permanent cure.
Only symptomatic cure is given.
2) Acquired biotin deficiency
• TWO TYPES :
I. Leiner’s Disease
II. Egg-white Injury
19. • Leiner’s Disease
Seen in infants while being exclusively breast-
fed and infants having chronic diarrheas.
Due to chronic diarrhea, dietary biotin is not
absorbed.
Breast milk has low content of biotin.
Such infants present with manifestations of
biotin def. in form of dermatitis and easily
peeling of skin.
20. • Treatment :
Supplementation of biotin. However, primarily
the cause of the recurrent diarrhea has to be
treated.
Easy peeling of skin Leiner’s disease
21. Egg-white Injury
• Due to excessive consumption of raw eggs
mainly egg white.
• Protein Avidin (anti-vitamin) binds with biotin
and inactivates it.
• Cooked egg-white is found not to be toxic
since Avidin is heat-liable and boiling of eggs
inactivates Avidin.
• 1 molecule of Avidin binds to 4 molecules of
biotin.
