Stimulates activity of the AccA3/AccD5 biotin-dependent acyl-CoA carboxylase complex (PubMed:16354663, PubMed:16385038). Interacts with AccD5 and modulates its carboxylase activity for acetyl-CoA and propionyl-CoA (PubMed:16354663, PubMed:16385038). Inhibits activity of the AccA3/AccD6 complex (PubMed:17114269). Is also required for the activity of the long-chain acyl-CoA carboxylase (LCC) complex (PubMed:28222482). Interacts with the AccA3/AccD5 biotin-dependent acyl-CoA carboxylase complex (PubMed:16354663, PubMed:16385038). Interacts with the AccA3/AccD6 complex (PubMed:17114269). Is also part of the long-chain acyl-CoA carboxylase (LCC) complex, which 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). Protein level is maximal in exponential growth phase and declines during late log and stationary phase. It is uncertain whether the five sets of tandem repeats at the N terminus are required, or not, for maximal enhancement of carboxylase activity.