Biotin attaches to the active site of four important enzymes. These enzymes are known as carboxylases. Each of these carboxyleses catalyze essential metabolic reactions. Biotin also affects replication and transcription of DNA. It acts as a carrier for carbon dioxide in the pyrubate carboxylase reaction, where biotin is linked to the epsilonamino group of a lysine residue in the enzyme. Biotin is necessary for both metabloism and growth in humans.