BIOTIN
Biotin is also known as vitamin H and coenzyme R (Hexahydro-2-oxo-1H-thienal[3,4-d]- imidazole-4-pentatonic acid). It is found primarily in liver, kidney and muscle. Biotin functions as an essential cofactor for four carboxylases that catalyze the incorporation of cellular bicarbonate into the carbon backbone of organic compounds. Acetyl-CoA carboxylase (ACC) is located in the cytosol where it catalyzes the formation of malonyl-CoA which then serves as a substrate for fatty acid elongation. The other three enzymes are located in the mitochondria. Pyruvate carboxylase (PC) catalyzes the incorporation of bicarbonate into pyruvate to form oxaloacetate, an intermediate in the tricarboxylic acid cycle. In gluconeogenic tissues such as the liver and kidney, oxaloacetate can be converted to glucose. Methcrotonyl-CoA carboxylase (MCC) catalyzes the incorporation of bicarbonate into propionyl-CoA to form methylmalonyl-CoA which, in turn, is metabolized to other compounds that eventually enter the tricarboxylic acid cycle.
Deficiencies: Severe deficiency causes 1) THINNING OF HAIR, loss of hair color, and eventually complete loss of hair; 2) a scaly, red rash distributed around the openings of the eyes, nose, mouth, and perineal area; and 3) central nervous system abnormalities such as depression, lethargy, hallucinations, and paresthesias. In infants, the neurologic findings include hypotonia, lethargy, and developmental delay, as well as a peculiar withdrawn behavior. In patients on total or near total intravenous feeding, an unusual distribution of facial fat coupled with the rash and hair loss produces a distinct appearance called "biotin deficiency facies
