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L-carnitine is an amino acid derivative (but not a true amino acid because true amino acid must possess an amino group and a carboxyl group at an alpha carbon) with a tertiary amine as a side chain. It is one of the essential compound needed for the fat metabolism. because its beta carbon is a chiral carbon, Carnitine exists in two stereoisomeric form L and D.
It is the L form that is essential for the fat metabolism. L-carnitine is synthesized in the liver and kidney with the help of two amino acids, methionine, and lysine. L-carnitine helps fat metabolism in the sense that free fatty acid released from the fat digestion are first acetylated and then transported into the mitochondrial matrix for further oxidation (beta oxidation).
Free fatty acids first react with the acetyl CoA Â and ATP to form a Fatty acyl-CoA catalyzed by the Fatty acyl-CoA Â synthetase located on outer mitochondrial matrix. Thus formed fatty acyl-CoA further reacts with L-carnitine to form Fatty acyl-L-carnitine catalyzed by the outer mitochondrial membrane enzyme, carnitine fatty-acyl-transferase I.
Now, fatty acyl-carnitine is ready to be transported to the mitochondrial matrix through the transporter carnitine-acylcarnitine translocase (an antiport that transports carnitine and fatty acyl-L-carnitine in an opposite direction. In this way, one residue of free fatty acid is transported into the mitochondrial matrix with the help of one molecule of L-carnitine.
In mitochondrial matrix, fatty acyl-L-carnitine is brokenÂ down into L-carnitine and fatty acyl-CoA catalyzed by carnitine fatty-acyl-transferase II (inner mitochondrial membrane enzyme) and thus release L-carnitine is transported back to the intermembrane space where it again reacts with a molecule of fatty acyl-CoA to form fatty acyl-L-carnitine to be transported back into the mitochondrial matrix.
This is how L-carnitine aids fatty acid metabolism and, therefore, deficiency of the L-carnitine may impair the fatty acid metabolism.