carnitine

A trimethylammonium (betaine) derivative of γ-amino-β-hydroxybutyric acid, formed from N^ε,N^ε,N^ε-trimethyllysine and from γ-butyrobetaine; the l-isomer is a thyroid inhibitor found in muscle, liver, and meat extracts; l-c. is an acyl carrier with respect to the mitochondrial membrane; it thus stimulates fatty acid oxidation. SYN: B_T factor, vitamin B_T. [L. caro carn-, flesh + ine]

- c. acetyltransferase an enzyme found in mitochondria that catalyzes the reversible transfer of an acetyl group from acetyl-CoA to c., forming O-acetylcarnitine and coenzyme A. Acetylcarnitine is an important fuel source in sperm.

- c. acylcarnitine translocase a transport protein found in the inner mitochondrial membrane. Transports acylcarnitine derivatives into the mitochondria and transports c. out of the mitochondria. An important step in fatty acid oxidation.

- c. palmitoyltransferase 1. an enzyme that reversibly forms acylcarnitines and coenzyme A from c. and acylcoenzyme A (often, palmitoyl-CoA); important in fatty acid oxidation. Deficiency of isozyme I results in ketogenesis with hypoglycemia; deficiency of isozyme II affects primarily skeletal muscle.

* * *

car·ni·tine 'kär-nə-.tēn n a quaternary ammonium compound C₇H₁₅NO₃ that is present esp. in vertebrate muscle, is involved in the transfer of fatty acids across mitochondrial membranes, and in humans is obtained from food (as meat or milk) or is synthesized from a lysine derivative

* * *

car·ni·tine (kahrґnĭ-tēn) a betaine derivative found in skeletal muscle and liver; it is required for mitochondrial beta oxidation of fatty acids, carrying the acyl groups (fatty acids) across the mitochondrial membrane to the matrix, where they are transferred back to coenzyme A prior to oxidation. It has been used as an investigational antithyroid and antiangina agent. Deficiency of carnitine leads to buildup of fatty acids in the body.