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. 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. Lipid metabolism; fatty acid biosynthesis. Lipid metabolism; mycolic acid biosynthesis. The biotin-dependent acyl-CoA carboxylase complex is composed of AccA3, which contains the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains, and an AccD protein, which contains the carboxyl transferase (CT) domain.