Inter-tissue relationships in the synthesis and distribution of carnitine.

Carnitine (3-hydroxy-4-trimethylammonio-butanoate), an essential cofactor for mitochondrial long-chain fatty acid oxidation, is synthesized in mammals, and consequently is present in diets containing meat products. When the diet does not contain carnitine rats and man appear to produce sufficient carnitine to maintain homoeostatis. Carnitine is the product of the essential amino acids lysine and methionine. Specific lysinyl residues (in peptide-linkage) are methylated in the 6-amino position. After proteolysis, N 6 trimethyl-lysine is released and converted, ultimately, into carnitine. Although the metabolic intermediates for the formation of carnitine have been characterized, the intertissue relationships of these intermediates have not been fully established.