Biotinidase, also known as biotinase and BTD, is a ubiquitous mammalian cell enzyme which expressed at high levels in the liver, serum, and kidney. Its primary function is to cleave biotin from biocytin, preserving the pool of biotin for use as a cofactor for biotin dependent enzymes, namely the 4 human carboxylases. Biotinidase also recycles biotin from enzymes in the body that use it as a helper component in order to function. These enzymes, known ascarboxylases, are important in the processing of fats, carbohydrates, and proteins. Biotin is attached to these carboxylase enzymes through an amino acid (the building material of proteins) called lysine, forming a complex calledbiocytin.