l‐carnitine: Structure and Function

l-carnitine is found in nearly all living cells. l-carnitine present in human body can be either provided by a biosynthetic pathway or by food. Carnitine plays a major role in lipid and energy metabolism. In the human body, the primary role of l-carnitine is to shuttle long-chain fatty acids into the mitochondria where they are used to produce energy. l-carnitine is also involved in the peroxisomal oxidative metabolism and serves as a cofactor for various enzymatic reactions. Several reports suggest that l-carnitine may act as an anti-oxidant agent and limit the deleterious effects of free radicals. Many studies have estimated the role and the potential effectiveness of l-carnitine in various physiological and pathophysiological states such as physical exercise, heart disease, aging, weight management and brain function. A deficiency in l-carnitine has marked effects on the function of skeletal muscle, heart and nervous cells.

Key Concepts:

  • Carnitine is a cofactor for many enzymatic reactions.
  • Carnitine regulates various physiological functions.
  • Carnitine may limit ROS attack.

Keywords: l-carnitine; lipid metabolism; mitochondria; peroxisome; muscle; physiology; nutrition

Figure 1. Schematic representation of l-carnitine and l-carnitine esters. In the top part of the figure is represented free carnitine, in the bottom part, R represents an acyl group that can be an acetyl, a propionyl group or any other acyl group.
Figure 2. Carnitine biosynthesis. Several enzymatic reactions are needed for l-carnitine synthesis. (1) Lysyl methyltransferases, (2) trimethyllysine dioxygenase, (3) hydroxyl N-trimethyllysine aldolase, (4) 4-trimethylammoniobutyraldehyde dehydrogenase and (5) -butyrobetaine hydroxylase.
Figure 3. The carnitine system. This enzymatic system is involved in the entry of fatty acids into the mitochondrial matrix. Several proteins compose this system: ACS, acyl-CoA synthase; CACT, carnitine acylcarntine tranlocase and CPT, carnitine palmitoyltranferase.
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 Further Reading
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    Wallace DC, Fan W and Procaccio V (2010) Mitochondrial energetics and therapeutics. Annual Review of Pathology 5: 297–348.
    Zammit VA, Ramsay RR, Bonomini M and Arduini A (2009) Carnitine, mitochondrial function and therapy. Advanced Drug Delivery Reviews 61(14): 1353–1362.
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Demarquoy, Jean(Jan 2011) l‐carnitine: Structure and Function. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023200]