The enzyme catalyses the transfer of a carboxyl group carried on a biotinylated biotin carboxyl carrier protein (BCCP) to acetyl-CoA, forming malonyl-CoA. In some organisms this activity is part of a multi-domain polypeptide that includes the carrier protein and EC 22.214.171.124
, biotin carboxylase (see EC 126.96.36.199
, acetyl-CoA carboxylase). Some enzymes can also carboxylate propanonyl-CoA and butanoyl-CoA (cf. EC 188.8.131.52
, propionyl-CoA carboxylase).