Carnitine shuttle. Scheme of the carnitine shuttling system. Activated fatty acid (CoA~FA) are transferred to carnitine (C) via carnitine-acyltransferase [I] at the cytoplasm. The carnitine-fatty acid complex (C~FA) is then shuttled via a so called antiporter [II] into the mitochondria in exchange for a free carnitine. There, a mitochondrial isoform of the carnitine-acyltransferase [III] reactivates via Coenzyme A (CoA) the fatty acids. The activated fatty acid inside the mitochondria is a precursor for β-oxidation. Note that reactions [I] and [III] are reversible.