Carnitine shuttle mechanisms

Long-chain fatty acids can slowly cross the mitochondrial membrane by themselves, but this is too slow to keep up with their metabolism. The carnitine shuttle provides a transport mechanism and allows control of (3 oxidation. Malonyl-CoA, a precursor for fatty acid synthesis, inhibits the carnitine shuttle and slows down (3 oxidation (Fig. 13-5). 

Carnitine is part of the shuttle mechanism whereby long-chain fatty acids are made into acyl carnitine derivatives and transport across the mitochondrial membrane, which is impermeable to long-chain fatty acids per se and to their coenzyme A esters. Once across the membrane, the acylcar-nitines are reconverted to their fatty acid CoA form and undergo beta-oxidation to liberate energy. 

Triglycerides are made up of three FAs attached to one molecule of glycerol. Short-chain FAs may cross the inner mitochondrial membrane. Carnitine is not an FA, but is part of the shuttle mechanism that passes acyl CoA molecules into mitochondria. FAs are broken down by P-oxidation to form acetyl CoA. 

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