carnitine, a water-soluble, vitamin-like compound related to the amino acids. It is an essential growth factor for mealworms and is present in striated (striped) muscle and liver tissue of higher animals. Carnitine, which can be synthesized by the higher animals, is associated with the transfer of fatty substances from the bloodstream to active sites of fatty-acid oxidation within muscle cells. It regulates the rate of oxidation of fatty acids and may afford the means by which a cell can rapidly shift its metabolic patterns (e.g., from fat synthesis to fat breakdown).