Vitamin B7

INTRODUCTION:

Vitamin B7, more commonly known as biotin, is a water-soluble vitamin that is vital for the body’s metabolism and functioning. It is an essential component of a number of enzymes responsible for several crucial metabolic pathways in the human body, including the metabolism of fats and carbohydrates, as well as amino acids involved in protein synthesis.

Biotin is known to promote cell growth and is often a component of dietary supplements used for strengthening hair and nails, as well as those marketed for skin care. 

CHEMICAL NAME:

5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid

STRUCTURE:

SOURCES OF VITAMIN B7:

Vitamin B7 is found in a number of foods, though in small amounts. This includes walnuts, peanuts, cereals, milk, and egg yolks. Other foods that contain this vitamin are whole meal bread, salmon, pork, sardines, mushroom and cauliflower. Fruits that contain biotin include avocados, bananas and raspberries. In general, a healthy varied diet provides the body with sufficient amounts of biotin.

 

RECOMMENDED INTAKE OF VITAMIN B7:

PHYSIOLOGICAL ROLE OF VITAMIN B7:

Vitamin B7 promotes appropriate function of the nervous system and is essential for liver metabolism as well. Biotin is commonly advised as a dietary supplement for strengthening hair and nails, as well as in skin care. It is suggested that biotin aids cell growth and the maintenance of mucous membranes. Your body needs biotin to help convert certain nutrients into energy. It also plays an important role in the health of your hair, skin, and nails.

MECHANISM OF ACTION OF VITAMIN B7 :

Biotin is the prosthetic group of certain enzymes that catalyse CO2-transfer reaction (CO2 fixation reaction). In biologic system, biotin functions as the coenzyme for the enzyme called carboxylases, which catalyse the CO2-fixation (Carboxylation).

In this process, Biotin is first converted to carboxybiotincomplex by reaction with HCO3 – and ATP. “CO2-biotin complex’’ is the source of “active” CO2 which is transferred to the substrate, CO2 becomes attached to the biotin coenzyme as shown below.

Examples of carboxylation or “CO2-fixation” reactions in biologic systems are given in box.

CO2 fixation reactions

• Conversion of acetyl-CoA to Malonyl-CoA: In the first step of extra mitochondrial ‘de Novo’ FA synthesis, the acetyl- CoA is converted to Malonyl-CoA, the reaction is catalyzed by the enzyme acetyl-CoA carboxylase.

• Conversion of propionyl-CoA to methylmalonyl-CoA:

The enzyme catalysing the reaction is propionyl-CoA carboxylase.

• Conversion of pyruvic acid to oxalo-acetate: The enzyme that catalyzes the reaction is Pyruvate carboxylase. Other reactions where Biotin has been incriminated are:

• Conversion of β-methyl crotonyl-CoA to β-methyl glutaconyl-

CoA:

 In their conversion in leucine metabolism, the reaction is catalysed by the enzyme β-methyl-erotonyl-CoA carboxylase.

Vitamin B7 Deficiency

Overt biotin deficiency is very rare in humans. However, marginal biotin deficiency can be measured by several indicators such as reduced propionyl-CoA carboxylase (PCC) activity in peripheral blood lymphocytes and reduced urinary excretion of biotin

Causes/ Risk factors

Deficiency has been shown during prolonged intravenous (‘parenteral’) feeding without vitamin B7 supplementation and consumption of raw egg white for a prolonged period (many weeks to years), since an antimicrobial protein found in raw egg white (avidin) binds biotin and prevents its absorption . Cooking denatures avidin, making it digestible and hence stops its interference with the biotin absorption . Research suggests that a substantial number (at least one-third) of women develop marginal biotin deficiency during normal pregnancy because the rapidly growing fetus requires biotin for the synthesis of essential biotin-dependent enzymes and proteins.

Symptoms

Signs of overt biotin deficiency include hair loss and a characteristic scaly red rash in the face (around the eyes, nose, mouth), and in the genital area. Neurologic symptoms in adults have included depression, lethargy, hallucination, numbness and tingling of the extremities, and ataxia

Treatment

Biotinidase deficiency is treated with oral biotin (vitamin H; coenzyme R, part of vitamin B complex) supplements. Treatment should begin as soon as the diagnosis is made. With biotin treatment, symptoms of the disorder may disappear.