Activation of long-chain fatty acids for both synthesis of cellular lipids, and degradation via beta-oxidation (Probable). Preferentially uses palmitate, palmitoleate, oleate, linoleate and eicosenoate as substrates (PubMed:12177484, PubMed:12366803). Can use myristate and linolenate as substrates (PubMed:12366803). May play a regulatory role both in fatty acid import into glyoxysomes and in fatty acid beta-oxidation (PubMed:12481085). Functions redundantly with LACS7 in lipid mobilization for beta-oxidation during seed germination, which is essential for postgerminative growth and seedling establishment (PubMed:14742880, PubMed:16844736). a long-chain fatty acid + ATP + CoA = a long-chain fatty acyl-CoA + AMP + diphosphate ATP + CoA + tetradecanoate = AMP + diphosphate + tetradecanoyl-CoA ATP + CoA + hexadecanoate = AMP + diphosphate + hexadecanoyl-CoA (9Z)-octadecenoate + ATP + CoA = (9Z)-octadecenoyl-CoA + AMP + diphosphate (9Z,12Z)-octadecadienoate + ATP + CoA = (9Z,12Z)-octadecadienoyl-CoA + AMP + diphosphate (9Z,12Z,15Z)-octadecatrienoate + ATP + CoA = (9Z,12Z,15Z)-octadecatrienoyl-CoA + AMP + diphosphate Lipid metabolism; fatty acid metabolism. Expressed in roots, stems, leaves flowers and germinating seedling (PubMed:12177484). Preferentially expressed in seeds and senescent leaves. Induced during seed germination. Up-regulated by ozone. Seedlings of the lacs6 and lacs7 double mutant were arrested in postgerminative growth due to inability to mobilize fatty acids for beta-oxidation, a necessary process to pursue the development. Belongs to the ATP-dependent AMP-binding enzyme family.