CARNITINE:
A. History. Carnitine has long been known as a constituent of meat extractives. Its vitamin nature was first recognized when it was shown to be an essential food factor of certain insects such as the yellow mealworm, Tenebrio molitor. It was, however, first isolated from muscles.
B. Occurrence. Carnitine is widely distributed in most tissues including plants, animals and microorganisms. It occurs in the free state and also bound to lipid.
C. Structure. Carnitine is a betaine (pronounced as ‘bay-tah-een’).
D. Metabolism. Fatty acids are activated on the outer mitochondrial membrane whereas they
are oxidized in the mitochondrial matrix. Since the inner mitochondrial membrane is impermeable to long-chain acyl CoA molecules, a special transport mechanism is needed for them. It has been suggested that carnitine acts as a carrier of the activated long-chain fatty acids across the inner mitochondrial membrane. The acyl group is transferred from the S atom of acyl CoA to the OH group of carnitine to produce acyl carnitine, which traverses the inner mitochondrial membrane. In the mitochondrial matrix, the acyl group from acyl carnitine is transferred back to CoA so as to regenerate acyl CoA and free the carnitine. As the value of K is near 1, the O-acyl bond of carnitine is a high-energy bond. These transacylation reactions are reversible and are catalyzed by
fatty acyl CoA : carnitine fatty acid transferase.
A. History. Carnitine has long been known as a constituent of meat extractives. Its vitamin nature was first recognized when it was shown to be an essential food factor of certain insects such as the yellow mealworm, Tenebrio molitor. It was, however, first isolated from muscles.
B. Occurrence. Carnitine is widely distributed in most tissues including plants, animals and microorganisms. It occurs in the free state and also bound to lipid.
C. Structure. Carnitine is a betaine (pronounced as ‘bay-tah-een’).
D. Metabolism. Fatty acids are activated on the outer mitochondrial membrane whereas theyare oxidized in the mitochondrial matrix. Since the inner mitochondrial membrane is impermeable to long-chain acyl CoA molecules, a special transport mechanism is needed for them. It has been suggested that carnitine acts as a carrier of the activated long-chain fatty acids across the inner mitochondrial membrane. The acyl group is transferred from the S atom of acyl CoA to the OH group of carnitine to produce acyl carnitine, which traverses the inner mitochondrial membrane. In the mitochondrial matrix, the acyl group from acyl carnitine is transferred back to CoA so as to regenerate acyl CoA and free the carnitine. As the value of K is near 1, the O-acyl bond of carnitine is a high-energy bond. These transacylation reactions are reversible and are catalyzed by
fatty acyl CoA : carnitine fatty acid transferase.
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