Possible functions of short-chain and medium-chain carnitine acyltransferases.
Several mammalian tissue contain water-soluble, branched chain acylcarnitines and other short-chain aliphatic acylcarnitines and also contain a broad spectrum of short-chain and medium-chain carnitine acyltransferase (CAT) activities. Although carnitine can stimulate the oxidation of branched chain alpha-ketoacids, it has not been established that carnitine is required for the oxidation of the alpha-ketoacids in the matrix of mitochondria. Rather it probably acts as a reversible sink for acyl residues, thereby generating CoASH, which can be used to maintain normal metabolism; thus carnitine would have a facilitative rather than an obligatory role. Microsomes and peroxisomes contain medium- and short-chain CATs. This occurrence is short- and medium-chain CATs in peroxisomes is consistent with carnitine's being involved in shuttling the chain-shortened products of beta-oxidation out of peroxisomes. Human urine contains a spectrum of short-chain acylcarnitines and data are presented that show a large amount of propionylcarnitine in the urine of the individual with a metabolic problem. The cumulative data are consistent with the conclusion that carnitine has multiple roles in mammalian metabolism, including the shuttling of beta-oxidation chain-shortened products out of peroxisomes in liver, the modulation of the acyl-CoA/CoASH ratio in mammalian cells, and the translocation of acetyl units for selective synthesis in a yeast.
D000105:Acetyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002331:Carnitine / Q000378:metabolism*; D002333:Carnitine Acyltransferases / Q000378:metabolism* / Q000652:urine; D005198:Fanconi Syndrome / Q000652:urine; D005227:Fatty Acids / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008830:Microbodies / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D008970:Molecular Weight; D010084:Oxidation-Reduction; D051381:Rats; D012756:Sheep; D013379:Substrate Specificity
D000596:Amino Acids; D005227:Fatty Acids; D000105:Acetyl Coenzyme A; D000217:Acyltransferases; D002333:Carnitine Acyltransferases; D002331:Carnitine