It is a colorless need like crystals. It is only slightly soluble in water and is heat stable. It is monocarboxylic acid.

   Occurrence of Biotin

 It is widely distributed in nature; it is found specifically in liver, kidney milk, tomatoes, yeast and molasses. Biotin occurs in large amounts in royal jelly produced by bees. It is also synthesized by intestinal flora and this seems a more important source of biotin than the diet.

   Biochemical Role of Biotin

Biotin acts as a coenzyme in reactions involving a fixing of CO2 which is first taken up by this vitamin. This is shown as below.
The biotin-CO2 complex then passes its CO2 to the substrate and biotin is liberated. The following reactions (carboxylations) need biotin as a coenzyme.
Conversion of Acetyl-S-ACP to malonyl-S-A-CP. This the first step in the cytoplasmic biosynthesis of fatty aicd.

   Conversion of pyruvic acid to oxaloacetic acid

Formation of carbamyl phosphate from NH3CO2 and ATP: Carbamyle phosphate takes part in the synthesis of pyrimidine and arginine. Arginine on hydrolysis gives rise to urea.
Biotin also takes part in the biosynthesis of purines.

   Deficiency Symptoms of Biotin

Deficiency of Biotin is rarely seen clinically but can be produced experimentally. If volunteers are fed a large amount of raw egg white. A glycoprotein named avidin (meaning hungury) which is strongly basic is present in raw egg white takes up all Biotine and forms a biotin-avidin complex. This cannot be hydrolyzed by proteases or even by acids and therefore the ingested biotin is not absorbed. One molecule of avidin combines with 2 molecules of biotin. Symptoms of deficiency are lassitude, skin disorders, anemia and muscles pain.