L-Palmitoylcarnitine or hexadecanoylcarnitine is an acylcarnitine. It is technically a long-chain acyl fatty acid derivative ester of carnitine which facilitates the transfer of long-chain fatty acids from cytoplasm into mitochondria during the oxidation of fatty acids. The general role of acylcarnitines is to transport acyl-groups, organic acids and fatty acids, from the cytoplasm into the mitochondria so that they can be broken down to produce energy. As part of this process, palmitic acid is first transported into the cell via the long-chain fatty acid transport protein 1 (FATP1). Once inside the cell it undergoes a reaction to form an acyl-CoA derivative called palmitoyl-CoA. This reaction is facilitated by the Long-chain fatty-acid CoA ligase 1 protein, which adds a CoA moiety to appropriate acyl groups. Many acyl-CoA groups will then further react with other zwitterionic compounds such as carnitine (to form acylcarnitines) and amino acids (to form acyl amides). The carnitine needed to form acylcarnitines inside the cell is transported into the cell by the organic cation/carnitine transporter 2.  In forming an acylcarnitine derivative, palmitoyl-CoA reacts with L-carnitine to form palmitoylcarnitine. This reaction is catalyzed by carnitine O-palmitoyltransferase. This enzyme resides in the mitochondrial outer membrane. While this reaction takes place, the palmitoylcarnitine is moved into the mitochondrial intermembrane space. Following the reaction, the newly synthesized acylcarnitine is transported into the mitochondrial matrix by a mitochondrial carnitine/acylcarnitine carrier protein found in the mitochondrial inner membrane. Once in the matrix, palmitoylcarnitine can react with the carnitine O-palmitoyltransferase 2 enzyme found in the mitochondrial inner membrane to once again form palmitoyl-CoA and L-carnitine. Palmitoyl-CoA then enters into the mitochondrial beta-oxidation pathway to form aceytl-CoA. Acetyl-CoA can go on to enter the TCA cycle, or it can react with L-carnitine to form L-acetylcarnitine in a reaction catalyzed by Carnitine O-acetyltransferase. This reaction can occur in both directions, and L-acetylcarnitine and CoA can react to form acetyl-CoA and L-carnitine in certain circumstances. Finally, acetyl-CoA in the cytosol can be catalyzed by acetyl-CoA carboxylase 1 to form malonyl-CoA, which inhibits the action of carnitine O-palmitoyltransferase 1, thereby preventing palmitoylcarnitine from forming and thereby preventing it from being transported into the mitochondria.  L-Palmitoylcarnitine has been also reported to change the activity of certain proteins and to stimulate the activity of caspases 3, 7, and 8. Interestingly, the level of this long-chain acylcarnitine has been shown to increase during apoptosis. Palmitoylcarnitine has also been reported to diminish the binding of phorbol esters (protein kinase C activators) and the autophosphorylation of the enzyme. Some of the physicochemical properties of palmitoylcarnitine may help to explain the need for coenzyme A-carnitine-coenzyme A acyl exchange during mitochondrial fatty acid import. The amphiphilic character of palmitoylcarnitine may also explain its proposed involvement in the pathogenesis of myocardial ischemia. L-Palmitoylcarnitine accumulates in ischemic myocardium and potentially contributes to myocardial damage through alterations in membrane molecular dynamics. This is a mechanism through which could play an important role in ischemic injury (PMID: 2540838, 15363641, 8706815). Palmitoylcarnitine is characteristically elevated in late-onset carnitine palmitoyltransferase II deficiency (OMIM: 255110).