Fatty acids are activated via the creation of a thioester bond with CoA in the cytosol to form acyl-CoA prior to being transported into the mitochondria. This is an ATP-dependent process carried out by acyl-CoA synthetases and the presence of CoA-SH. The long chain fatty-acyl-CoA then becomes altered by carnitine palmitoyltransferase 1 to acylcarnitine and is able to move across the mitochondrial membrane through carnitine translocase.