5-hydroxyhexanoylcarnitine is an acylcarnitine. 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, 5-hydroxyhexanoic 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 5-hydroxyhexanoyl-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, 5-hydroxyhexanoyl-CoA reacts with L-carnitine to form 5-hydroxyhexanoylcarnitine. This reaction is catalyzed by carnitine O-palmitoyltransferase. This enzyme resides in the mitochondrial outer membrane. While this reaction takes place, the 5-hydroxyhexanoylcarnitine 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, 5-hydroxyhexanoylcarnitine can react with the carnitine O-palmitoyltransferase 2 enzyme found in the mitochondrial inner membrane to once again form 5-hydroxyhexanoyl-CoA and L-carnitine. 5-hydroxyhexanoyl-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 5-hydroxyhexanoylcarnitine from forming and thereby preventing it from being transported into the mitochondria.

Acylcarnitine 5-hydroxyhexanoylcarnitine References