Component of the acetyl coenzyme A carboxylase (ACC) complex. Biotin carboxylase (BC) catalyzes the carboxylation of biotin on its carrier protein (BCCP) and then the CO(2) group is transferred by the transcarboxylase to acetyl-CoA to form malonyl-CoA. acetyl-CoA + N(6)-carboxybiotinyl-L-lysyl-[protein] = malonyl-CoA + N(6)-biotinyl-L-lysyl-[protein] Binds 1 zinc ion per subunit. Lipid metabolism; malonyl-CoA biosynthesis; malonyl-CoA from acetyl-CoA: step 1/1. Acetyl-CoA carboxylase is a heterohexamer composed of biotin carboxyl carrier protein (AccB), biotin carboxylase (AccC) and two subunits each of ACCase subunit alpha (AccA) and ACCase subunit beta (AccD). It is not known from which strain the crystal structure is derived. Belongs to the AccD/PCCB family.