Acyl-CoA synthetases, also known as acyl-CoA ligases, are enzymes that "activate" fatty acids by thioesterification to coenzyme A. It represents the initial step of fatty acid metabolism so that fatty acids can participate in catabolic and anabolic pathways. Among these are, for example, the synthesis of triacylglycerol, phospholipids, plasmalogens, sphingolipids, the degradation of fatty acids for energy production, the conversion to alcohols or aldehydes, the elongation of fatty acids, the insertion and removal of double bonds or the covalent binding to proteins.