Biotin: Chemistry, Absorption and Functions | Vitamins

In this article we will discuss about Biotin:- 1. Introduction to Biotin 2. Chemistry of Biotin 3. Absorption and Storage 4. Daily Requirements 5. Normal Concentration 6. Functions 7. Deficiency Symptoms.

Contents:

1. Introduction to Biotin
2. Chemistry of Biotin
3. Absorption and Storage of Biotin
4. Daily Requirements of Biotin
5. Normal Concentration of Biotin
6. Functions of Biotin
7. Deficiency Symptoms of Biotin

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1. Introduction to Biotin:

a. Boas (1927) observed that when raw egg white was given as the main source of pro­tein in the diets of rats, they developed symptoms of dermatitis, retarded growth, loss of hair and loss of muscular control. All these symptoms were prevented by egg yolk. The factor was called ‘anti-egg while injury factor.

b. In 1931, Gyorgy named this factor ‘vita­min H’.

c. In 1939, vitamin H was isolated by Gyorgy, Kuhn and Lederer.

d. In 1942, Melville et al isolated vitamin H from milk and named this vitamin ‘Biotin’.

e. Biotin is widely distributed in many foods as biocytin which is released on proteoly­sis. It is synthesized by intestinal flora in excess of requirements. Deficiency is un­known except a very small number of peo­ple who eat abnormally large amounts of uncooked egg white which contains avidin that binds biotin and renders it una­vailable for absorption.

2. Chemistry of Biotin:

The chemical structure of biotin in the free state is given (Fig. 15.24).

The carboxyl group of biotin combines with the terminal nitrogen of lysine resi­due of enzyme protein forming biocytin (Lysine-biotin conjugate).

It is highly soluble in hot water.

It forms salts with alkali hydroxides.

It is stable to autoclaving at 120°C for 30 minutes at neutral pH.

3. Absorption and Storage of Biotin:

Biotin is readily absorbed from the small in­testine through the portal vein into the general cir­culation.

Excess of the requirements is not stored in the body but is mostly excreted in the urine.

4. Daily Requirements of Biotin:

5. Normal Concentration of Biotin in Blood:

12-24 µg/dl in adults.

14-55 µg/dl in infants.

6. Functions of Biotin:

Coenzyme activities:

Biotin is connected with the carboxylation reactions (CO₂ “fixation”). The biotin coenzyme- apoenzyme complex attaches CO₂ which is after­wards transferred to other substances.

The follow­ing reactions are accomplished by this mechanism:

a. Biotin acts as coenzyme along with acetyl-CoA carboxylase to convert acetyl-CoA to malonyl-CoA which is an impor­tant step for fatty acid synthesis in extra mitochondrial pathway.

b. The conversion of pyruvate to oxaloace­tate is also a biotin-dependent carboxyla­tion reaction catalyzed by pyruvate car­boxylase.

c. Biotin acts as a coenzyme in the conver­sion of propionic acid to succinic acid.

d. Biotin is involved in the fixation of CO₂ for the formation of carbon 6 in purine synthesis.

e. Succinic acid dehydrogenase, succinic acid decarboxylase, aspartic acid deami­nase, serine deaminase and threonine deaminase are influenced by biotin.

f. β-methylcrotonyl-CoA-carboxylase con­verts β-methylcrotenyl-CoA to P-methyl- glutacronyl-CoA in presence of biotin.

7. Deficiency Symptoms of Biotin:

The deficiency of Biotin may result from the destruction of intestinal bacteria by sulfonamide drugs or from the adequate intake of raw egg white which contains the protein avidin (interfere absorp­tion of biotin) in association with diarrhoea in case of infants. The deficiency develops nausea, anorexia, anemia, muscular pain, dermatitis of extremities.