Catalyzes the esterification, concomitant with transport, of exogenous long-chain fatty acids into metabolically active CoA thioesters for subsequent degradation or incorporation into phospholipids. Activity is the highest with fatty acid substrates of > 10 carbon atoms (PubMed:15213221). Is involved in the aerobic beta-oxidative degradation of fatty acids, which allows aerobic growth of E.coli on fatty acids as a sole carbon and energy source (PubMed:12535077). a long-chain fatty acid + ATP + CoA = a long-chain fatty acyl-CoA + AMP + diphosphate ATP + CoA + hexadecanoate = AMP + diphosphate + hexadecanoyl-CoA ATP + CoA + dodecanoate = AMP + diphosphate + dodecanoyl-CoA (9Z)-octadecenoate + ATP + CoA = (9Z)-octadecenoyl-CoA + AMP + diphosphate ATP + CoA + tetradecanoate = AMP + diphosphate + tetradecanoyl-CoA ATP + CoA + decanoate = AMP + decanoyl-CoA + diphosphate ATP + CoA + octanoate = AMP + diphosphate + octanoyl-CoA Optimum pH is 7.5-7.8. Lipid metabolism; fatty acid beta-oxidation. Homodimer. Partially membrane-associated. Well expressed during log and stationary phase aerobic growth but only poorly expressed during anaerobic growth (at protein level); aerobic expression is suppressed by glucose or C8 fatty acids (PubMed:15213221). Post-translationally cleaved by OmpT (PubMed:15213221). Cells lacking this gene are completely blocked in aerobic growth on fatty acids. The double fadD fadK deletion mutant fails to grow on fatty acids under either aerobic or anaerobic conditions, although fadD mutants grow on fatty acids under anaerobic conditions. The enzymatic mechanism is a two-step reaction that proceeds via the intermediate formation of an acyl-adenylate (acyl-AMP) intermediate. Belongs to the ATP-dependent AMP-binding enzyme family.