Catalyzes the activation of fatty acids by CoA to produce an acyl-CoA, the first step in fatty acid metabolism (PubMed:11470804, PubMed:12709059). Capable of activating medium-chain fatty acids (e.g. butyric (C4) to decanoic (C10) acids), and certain carboxylate-containing xenobiotics, e.g. benzoate (PubMed:11470804, PubMed:12709059). Also catalyzes the activation of lipoate to lipoyl-nucleoside monophosphate (By similarity). Activates lipoate with GTP at a 1000-fold higher rate than with ATP and activates both (R)- and (S)-lipoate to the respective lipoyl-GMP, with a preference for (R)-lipoate (By similarity). a medium chain fatty acid + ATP + CoA = a medium-chain fatty acyl-CoA + AMP + diphosphate ATP + benzoate + CoA = AMP + benzoyl-CoA + diphosphate (R)-lipoate + GTP + H(+) = (R)-lipoyl-GMP + diphosphate ATP + CoA + octanoate = AMP + diphosphate + octanoyl-CoA ATP + CoA + decanoate = AMP + decanoyl-CoA + diphosphate ATP + CoA + dodecanoate = AMP + diphosphate + dodecanoyl-CoA ATP + CoA + tetradecanoate = AMP + diphosphate + tetradecanoyl-CoA ATP + CoA + hexanoate = AMP + diphosphate + hexanoyl-CoA ATP + butanoate + CoA = AMP + butanoyl-CoA + diphosphate ATP + CoA + hexadecanoate = AMP + diphosphate + hexadecanoyl-CoA Monomer. Highly expressed in liver and kidney. Belongs to the ATP-dependent AMP-binding enzyme family.