Successfully reported this slideshow.
You’ve unlocked unlimited downloads on SlideShare!
• 2 rings : Imidazole ring & thiophenederivative.• Occurs in free form & bound form in tissuesand food.• Exists as biocytin, oxybiotin and desthiobiotinin bound form.
• Depending on the side chain :1. Alpha-biotin2. Beta biotino Covalently attached to epsilon amino groupof lysine to form biocytin (ε-N-Biotinyl lysine)• Biocytin is present in tissues.• Desthiobiotin and oxybiotin: These arebiologically active in certain strains of yeastand bacteria.
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 thenitrogen-fixing organisms.
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.
ExcretionIt is excreted in urine, faeces and in milksecretion.Metabolic role of biotin1. Biotin acts as coenzyme forcarboxylation reactions catalysed byCarboxylases.
• Biotin is first converted to carboxy-biotincomplex by reaction with bicarbonate & ATP.• CO2-biotin complex is the source of activeCO2 which is transferred to the substrate.
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 thefunctioning of TCA cycle depending on need of cell.
2) Carboxylation of propionyl coABiological significance• Succinyl CoA enters TCA cycle for complete oxidation toprovide energy.• Propionyl CoA is glucogenic in nature.
3) Conversion of Acetyl CoA to Malonyl CoABiological Significance• First &rate limiting reaction of FA biosynthesis.• In absence of biotin, FA synthesis is enormously affected.
4) Carboxylation of B-methyl crotonyl CoABiological Significance• Important reaction of Leucine Metabolism.• Biotin deficiency impairs leucine metabolism greatly.
Role of Biotin in cell division• Required for cell division & tissueproliferation.• Has an active role in maintaining texture ofskin, hair and nails. (Beauty vit)
Deficiency of BiotinVery rareOccurs except under 2 conditions:1. Congenital deficiency• It is due to deficiency of enzymeholocarboxylase synthetase.
Deficiency of the HCS enzyme makes thecarboxylases inefficient, precipitating all themanifestations of biotin deficiency.Also, CO2 transfer reactions are grosslyaffected.Clinical Manifestations• Growth retardation• Dermatitis• Loss of hair• Greying of hair• Abdominal discomfort and diarrhea
Treatment :No permanent cure.Only symptomatic cure is given.2) Acquired biotin deficiency• TWO TYPES :I. Leiner’s DiseaseII. Egg-white Injury
• Leiner’s Disease Seen in infants while being exclusively breast-fed and infants having chronic diarrheas. Due to chronic diarrhea, dietary biotin is notabsorbed. Breast milk has low content of biotin. Such infants present with manifestations ofbiotin def. in form of dermatitis and easilypeeling of skin.
• Treatment :Supplementation of biotin. However, primarilythe cause of the recurrent diarrhea has to betreated.Easy peeling of skin Leiner’s disease
Egg-white Injury• Due to excessive consumption of raw eggsmainly egg white.• Protein Avidin (anti-vitamin) binds with biotinand inactivates it.• Cooked egg-white is found not to be toxicsince Avidin is heat-liable and boiling of eggsinactivates Avidin.• 1 molecule of Avidin binds to 4 molecules ofbiotin.
References• Class Notes.• http://www.namrata.co/functions-of-biotin/• Wikipedia• Mn Rana Shinde