Biochemical function  Biotin is a water soluble vitamin and participates in transfer of carboxyl groups. Some enzymes that carry out carboxylation reactions are pyruvate carboxylase and acetyl CoA carboxylation. Pyruvate carboxylase is a high molecular weight enzyme which contains four molecules of biotin covalently attached to the enzyme protein through peptide bond with ε-amino group of lysine residue at the active site. Biotin and lysine are linked through peptide bond.
All biotin dependent carboxylases require ATP in all reactions. We can take the specific example of pyruvate decarvboxylases which catalyzes the reactions in two steps. In the first step the biotin-bound enzyme proteins removes CO₂ to form  carboxyl biotinyl enzyme:

In the next step the CO₂ moiety is transferred to an appropriate acceptor molecule depending upon the type of transcarboxylase involved. Pyruvate carboxylases requires an α-keto acid as an acceptor molecule.