On the rate-limiting step in the transfer of long-chain acyl groups across the inner membrane of brown adipose tissue mitochondria.
Brown adipose tissue mitochondria predominantly oxidize fatty acids in order to generate heat for non-shivering thermogenesis, and have an unusually high capacity for net transfer of long-chain fatty acyl groups from the outer to the inner (matrix) compartment. The activities of the "outer" and "inner" carnitine long-chain acyltransferases have been estimated in isolated mitochondria of cold-acclimated guinea pits by the continuous spectrophotometric recording of the redox level of flavoproteins in the acyl-CoA dehydrogenase pathway. This redox level is determined by the intramitochondrial content of acyl-CoA under the selected experimental conditions. The apparent initial rate of the "inner" acyltransferase (palmitoyl-L-carnitine added) is three order of magnitudes higher than the "outer" acyltransferase (palmitoyl-CoA added), and this difference is not influenced by the substrate concentration, pH and reaction temperature. Thus, the "outer" acyltransferase reaction is rate limiting in the transfer of long-chain acyl groups across the inner membrane of these mitochondria and catalyzes a non-equilibrium reaction in the intact organelle. Estimates of the absolute rate of the "outer" long-chain acyltransferase indicate that it exceeds that of rat liver mitochondria by a factor of 20.
D000064:Acclimatization; D044942:Acyl-CoA Dehydrogenase, Long-Chain / Q000378:metabolism*; D000217:Acyltransferases / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D001833:Body Temperature Regulation; D005227:Fatty Acids / Q000378:metabolism; D005420:Flavoproteins / Q000378:metabolism; D006168:Guinea Pigs; D008566:Membranes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction
D005227:Fatty Acids; D005420:Flavoproteins; D044942:Acyl-CoA Dehydrogenase, Long-Chain; D000217:Acyltransferases