Component of a biotin-dependent acyl-CoA carboxylase complex. This subunit catalyzes the ATP-dependent carboxylation of the biotin carried by the biotin carboxyl carrier (BCC) domain, resulting in the formation of carboxyl biotin. When associated with the beta1 subunit AccD1, is involved in branched amino-acid catabolism with methylcrotonyl coenzyme A as the substrate. ATP + hydrogencarbonate + N(6)-biotinyl-L-lysyl-[protein] = ADP + H(+) + N(6)-carboxybiotinyl-L-lysyl-[protein] + phosphate Binds 2 magnesium or manganese ions per subunit. Amino-acid degradation; L-leucine degradation. The biotin-dependent acyl-CoA carboxylase complex is composed of AccA1, which contains the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains, and AccD1, which contains the carboxyl transferase (CT) domain. The AccA1/AccD1 complex forms a dodecamer.