(organic chemistry) A betaine, 3-hydroxy-4-trimethylammonio-butanoate, that is found in the liver and has a function in fatty acid transport.
2014, Peggy R. Borum, Carnitine homeostasis in humans, Benjamin Toby Wall, Craig Porter (editors), Carnitine Metabolism and Human Nutrition, page 4,
Carnitine likely functions in maintaining homeostasis in many metabolic pathways and physiological conditions, with carnitine's role in energy metabolism homeostasis being the best studied.