Catalyzes the activation of medium/long-chain fatty acids as acyl-coenzyme A (acyl-CoA), which are then transferred to the multifunctional polyketide synthase (PKS) type III for further chain extension (PubMed:15042094, PubMed:19182784). Also involved in steroid side-chain degradation. Activates cholesterol metabolites with a C5 side chain, including cholate and chenodeoxycholate (PubMed:24244004). a medium chain fatty acid + ATP + CoA = a medium-chain fatty acyl-CoA + AMP + diphosphate a long-chain fatty acid + ATP + CoA = a long-chain fatty acyl-CoA + AMP + diphosphate ATP + CoA + hexanoate = AMP + diphosphate + hexanoyl-CoA ATP + CoA + dodecanoate = AMP + diphosphate + dodecanoyl-CoA ATP + CoA + hexadecanoate = AMP + diphosphate + hexadecanoyl-CoA ATP + cholate + CoA = AMP + choloyl-CoA + diphosphate ATP + chenodeoxycholate + CoA = AMP + chenodeoxycholoyl-CoA + diphosphate Lipid metabolism; fatty acid biosynthesis. Belongs to the ATP-dependent AMP-binding enzyme family.