L-Carnitine is a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine.
In eukaryotic cells, it is required for the transport of fatty acids from the intermembraneous space in the mitochondria, into the mitochondrial matrix during the breakdown of lipids (fats) for the generation of metabolic energy. It is widely available as a nutritional supplement. Carnitine was originally found as a growth factor for mealworms and labeled vitamin BT, although carnitine is not a proper vitamin. Carnitine exists in two stereoisomers: its biologically active form is L-carnitine, whereas its enantiomer, D-carnitine, is biologically inactive.