Biotin is a vitamin and a coenzyme commonly associated with enzymes performing carboxylation reactions. Biotin is typically linked covalently to carboxylase enzymes through the -amino nitrogen of lysine. Biotin is very tightly bound by avidin, a protein found in egg white. The strong interaction between these molecules is exploited in numerous purification techniques in biotechnology.

Enzymes containing biotin include acetyl CoA carboxylase, pyruvate carboxylase, and carbamoyl phosphate synthetase II