Required for maintaining the appropriate mycolic acid composition and permeability of the envelope on its exposure to acidic pH (PubMed:15937179). Catalyzes the activation of 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:19182784, PubMed:20027301, PubMed:22560731). It has preference for the fatty acid with long chain length in the following order: hexacosanoic acid (C26), tetracosanoic acid (C24) and palmitic acid (C16) (PubMed:20027301). a long-chain fatty acid + ATP + CoA = a long-chain fatty acyl-CoA + AMP + diphosphate ATP + CoA + hexacosanoate = AMP + diphosphate + hexacosanoyl-CoA ATP + CoA + tetracosanoate = AMP + diphosphate + tetracosanoyl-CoA ATP + CoA + hexadecanoate = AMP + diphosphate + hexadecanoyl-CoA ATP + CoA + dodecanoate = AMP + diphosphate + dodecanoyl-CoA kcat is 0.03 sec(-1) for palmitic acid (at pH 8 and at 37 degrees Celsius). Lipid metabolism; fatty acid biosynthesis. Homodimer. Membrane-associated through distinctive regions rich in arginine and aromatic residues. Expression is controlled by VirS. Induced at acidic pH and in macrophages. Inactivation of the mymA operon causes altered cell wall structure, reduced contents and altered composition of mycolic acids along with the accumulation of saturated C24 and C26 fatty acids, and enhanced susceptibility to antibiotics, detergents and acidic pH. Also impairs ability to survive in macrophages. Belongs to the ATP-dependent AMP-binding enzyme family.