The Biotin Carboxyl Carrier Protein is part of the enzyme Acetyl-CoA carboxylase and serves as a carrier protein for biotin and carboxybiotin throughout the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA in the first committed and rate regulating step of fatty acid biosynthesis.
References
Biotin carboxyl carrier protein Wikipedia(Text) CC BY-SA