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 (PubMed:16354663, PubMed:16385038, PubMed:17114269). When associated with the beta5 subunit AccD5, is involved in the carboxylation of acetyl-CoA and propionyl-CoA, with a preference for propionyl-CoA (PubMed:16354663, PubMed:16385038). When associated with the beta6 subunit AccD6, is involved in the carboxylation of acetyl-CoA and propionyl-CoA, with a preference for acetyl-CoA (PubMed:17114269). When associated with the beta4 subunit AccD4, the beta5 subunit AccD5 and the epsilon subunit AccE5, forms the LCC complex, which is involved in the carboxylation of long chain acyl-CoA (PubMed:16354663, PubMed:28222482). The LCC complex can use C16-C24 substrates, the highest specific activity is obtained with carboxy-C20-CoA (PubMed:28222482). 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. Carboxylase activity of the AccA3/AccD5 complex is stimulated by interaction with the epsilon subunit AccE5 (PubMed:16354663, PubMed:16385038). Activity of the AccA3/AccD6 complex is inhibited by interaction with AccE5 and by dimethyl itaconate, C75, haloxyfop, cerulenin, and 1,2-cyclohexanedione (PubMed:17114269). Lipid metabolism; fatty acid biosynthesis. Lipid metabolism; mycolic acid biosynthesis. Homodimer (PubMed:28469974). 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 (PubMed:16354663, PubMed:16385038, PubMed:17114269, PubMed:28222482). Can interact with AccD4, AccD5 and AccD6 (PubMed:16354663, PubMed:16385038, PubMed:17114269, PubMed:28222482). The AccA3/AccD5 complex forms a dodecamer, and can associate with the epsilon subunit AccE5 (Rv3280), which stimulates carboxylation by the complex (PubMed:16354663, PubMed:16385038). The AccA3/AccD6 complex forms a dodecamer. Interaction of AccA3/AccD6 with the epsilon subunit AccE5 (Rv3280) decreases carboxylation by the complex (PubMed:17114269). The long-chain acyl-CoA carboxylase (LCC) complex is composed of AccA3, AccD4, AccD5 and AccE5. The four subunits are essential for activity, but AccD5, together with AccE5, probably plays a structural role rather than a catalytic one (PubMed:28222482).