A. History: In 1935, Fritz Kögl, a Dutch biochemist,
isolated in crystalline form from 250 kg of dried egg yolks about 1 mg of a ‘bios’ factor (growth promoting factor) necessary for yeast
and named it as “biotin”.Four years later, Szent-Györgyi et al conclusively proved that biotin is synonymous to the “antiegg white injury factor” which is responsible for the cure of egg white injury, induced in rats and other animals by feeding them with raw egg white. The raw egg white contains a biotin-antagonist protein, avidin, which combines with biotin in a firm linkage to form a compound that cannot be absorbed by the intestine and is therefore, excreted. It is also called as coenzyme R because it is a growth factor for the nitrogen-fixing bacterium, Rhizobium.
isolated in crystalline form from 250 kg of dried egg yolks about 1 mg of a ‘bios’ factor (growth promoting factor) necessary for yeastand named it as “biotin”.Four years later, Szent-Györgyi et al conclusively proved that biotin is synonymous to the “antiegg white injury factor” which is responsible for the cure of egg white injury, induced in rats and other animals by feeding them with raw egg white. The raw egg white contains a biotin-antagonist protein, avidin, which combines with biotin in a firm linkage to form a compound that cannot be absorbed by the intestine and is therefore, excreted. It is also called as coenzyme R because it is a growth factor for the nitrogen-fixing bacterium, Rhizobium.
B. Occurrence: Biotin has a wide range of distribution both in the animal and the vegetable kingdoms. Yeast, liver, kidney, milk and molasses are among the richest sources ; peanuts and eggs have lesser amounts. Biotin occurs in nature usually in combined state as biocytin .
It is a bound form of biotin, linked as a peptide with the amino acid lysine.
C. Structure: The structure of biotin (C10H16O3N2S) was worked out by Vincent du Vigneaud in 1942. Biotin has an unusual structure and consists of a fused imidazole and thiophene ring with a fatty acid side chain. Two forms of biotin can exist, allobiotin and epibiotin. Biotin is optically active. Only the (+) biotin is active; the DL-biotin is half as active as the naturally occurring biotin. The oxybiotin, in which S atom of biotin is replaced with an O atom, has some activity.Biotin and thiamine are the only
sulfur-containing vitamins isolated to date.
It is a bound form of biotin, linked as a peptide with the amino acid lysine.C. Structure: The structure of biotin (C10H16O3N2S) was worked out by Vincent du Vigneaud in 1942. Biotin has an unusual structure and consists of a fused imidazole and thiophene ring with a fatty acid side chain. Two forms of biotin can exist, allobiotin and epibiotin. Biotin is optically active. Only the (+) biotin is active; the DL-biotin is half as active as the naturally occurring biotin. The oxybiotin, in which S atom of biotin is replaced with an O atom, has some activity.Biotin and thiamine are the only
sulfur-containing vitamins isolated to date.D. Properties: Biotin crystallizes as long needles. It is soluble in water and ethyl alcohol but is insoluble in chloroform and ether.It is heat-stable and is resistant to both acids and alkalies. It has a melting point of 230°C.
E. Metabolism: This vitamin serves as a prosthetic group for many enzymes. These biotincontaining enzymes catalyze the fixation of CO2 into organic molecules, thus bringing about carboxylation.
The carbon dioxide is carried as a carboxyl group attached to one of the ureidonitrogen atoms of biotin, forming N-carboxybiotin complex .They also bring about synthesis of fatty acids such as oleic acid.
E. Metabolism: This vitamin serves as a prosthetic group for many enzymes. These biotincontaining enzymes catalyze the fixation of CO2 into organic molecules, thus bringing about carboxylation.
The carbon dioxide is carried as a carboxyl group attached to one of the ureidonitrogen atoms of biotin, forming N-carboxybiotin complex .They also bring about synthesis of fatty acids such as oleic acid.F. Deficiency: In most animals including man, intestinal bacteria synthesize appreciable amounts of biotin. It is because of this reason that biotin-deficiency in human beings, fed on biotinfree diets, cannot be produced. However, biotin-deficiency may be induced by sterilization of intestine and by feeding with raw egg white. Avidin, the egg white protein, inactivates biotin by eliminating it from an otherwise complete diet. Such a deficiency in man leads to dermatitis, loss of hair, decrease in weight and edema. The lesions on skin appear with changes in posture and gait. These disorders may lead to death. Heating egg white destroys the avidin and prevents the so-called egg white injury. Brawny dermatitis, somnolence, hallucinations, and hyperesthesia with accumulation of organic acids are common. Other neurologic signs and defective immunity may occur.
G. Human requirements: The intestinal bacteria synthesize biotin in such appreciable amounts that the amount excreted in urine exceeds the intake. That is why the RDA for this vitamin has not been established. However, about 10 mg per day of biotin is sufficient for an adult.
H. Treatment : Parenteral solutions should contain biotin. Deficient patients respond to oral administration of 10 mg.
H. Treatment : Parenteral solutions should contain biotin. Deficient patients respond to oral administration of 10 mg.
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