l‐carnitine: Structure and Function

Abstract

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) γ‐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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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]