Biotin (Greek bios – life), vitamin H, vitamin B7 – heterocyclic organic chemical compound from the group of water-soluble vitamins. It contains a system of thiophene fused rings of imidazolidine and a carboxylic side chain. Occurs in animal and plant organisms. It is a coenzyme of several different enzymes. It is an essential component of biotin-dependent carboxylates. It participates in the transfer of the carboxylic group (-COO-) from the bicarbonate anion to various organic compounds, depending on the type of given carboxylase.
Biotin antivitamins are destiobiotine, dehydrobiotin, homobiotin and norbiotine.

The role in the body
Carboxylases are enzymes indispensable in many important biochemical reactions, e.g. in the process of glucose formation (gluconeogenesis), fatty acid synthesis or the citric acid cycle. Biotin also supports the function of the thyroid, the transformation of carbon dioxide, affects the proper functioning of the skin and hair, participates with vitamin K in the synthesis of prothrombin (one of the proteins involved in blood coagulation).

Biochemical mechanism of action of biotin as a coenzyme
Biotin, a co-enzyme of carboxylase, participates in the transfer of the carboxyl group to various organic compounds, i.e. in the carboxylation of these compounds. The bicarbonate, which is the source of the acid residue, first reacts with ATP. A mixed carbonate-phosphate anhydride is formed. The carbonate residue is then transferred to biotin – it joins the nitrogen atom in the heterocyclic ring. The carboxyl group is then transferred to the target molecule. The side chain present in the biotin molecule confers its elasticity (biotin is sometimes called the “elastic arm” of the carboxylase) and allows the bound carboxyl group to be moved a certain distance from the reaction site with the activated carbonate to the site of substantial carboxylation of the target molecule.

The effects of scarcity
Symptoms of biotin deficiency include skin lesions – rashes, inflammation, as well as hair loss, elevated cholesterol levels and inflammatory changes in the intestines. Due to the fact that biotin can be synthesized by the bacterial flora, its deficiency is very rare, usually under the influence of other factors than food deficiency (eg broad-spectrum antibiotics).

The effects of excess
No harmfulness for humans.

Biosynthesis
Plants and some microorganisms have the ability to synthesise biotin from pimelic acid (HOOC (CH2) 5COOH). Biosynthesis takes place in several stages with the participation of the following enzymes:
• 6-carboxyhexanoate CoA-ligase
• 8-amino-7-ketopelargonate synthase
• 8-amino-7-ketopelargonate aminotransferase
• detiobihotin synthase
• biotin synthase

Occurrence
Biotin occurs, among others in the liver, walnuts and earth, soy flour, egg yolk, crabs, almonds, sardines, mushrooms, brown rice, whole wheat flour, spinach, carrots, tomatoes.