-!- This enzyme is a multi-domain polypeptide that catalyzes three different activities - a biotin carboxyl-carrier protein (BCCP), a biotin carboxylase that catalyzes the transfer of a carboxyl group from hydrogencarbonate to the biotin molecule carried by the carrier protein, and the transfer of the carboxyl group from biotin to acetyl-CoA, forming malonyl-CoA. -!- In some organisms these activities are catalyzed by separate enzymes (see EC 6.3.4.14 and EC 2.1.3.15). -!- The carboxylation of the carrier protein requires ATP, while the transfer of the carboxyl group to acetyl-CoA does not.

-!- This enzyme, part of an acetyl-CoA carboxylase complex, acts on a biotin carboxyl-carrier protein (BCCP) that has been biotinylated by EC 6.3.4.15. -!- In some organisms the enzyme is part of a multi-domain polypeptide that also includes the carrier protein (e.g. mycobacteria). -!- Yet in other organisms (e.g. mammals) this activity is included in a single polypeptide that also catalyzes the transfer of the carboxyl group from biotin to acetyl-CoA (see EC 6.4.1.2).