Effect of palmitoyl-CoA and beta-oxidation of fatty acids on the kinetics of mitochondrial citrate transporter.
The kinetics of the hepatic mitochondrial citrate transporter were studied using 1,2,3-benzene tricarboxylate and the inhibitor-stop technique at 8 degrees C. The apparent Km for this transporter was 250 muM and the maximum velocity was 2 nmol of citrate transported per minute per milligram of mitochondrial protein. This apparent Km was increased when hepatic mitochondria were preincubated with both L-palmitoylcarnitine and CoA-SH but not with either alone. This rise in apparent Km was accompanied by a rise in the acid insoluble CoA-SH content. Removal of mitochondrial acid insoluble CoA by "defatted albumin" resulted in a parallel decrease in the apparent Km. The apparent Km for the citrate transporter was increased after coupled beta-oxidation of L-palmitoylcarnitine or octanoate without a detectable increase in acid insoluble CoA. Inhibition of beta-oxidation of L-palmitoylcarnitine by the D-derivative prevented the rise in the apparent Km. Preincubation with ATP resulted in an increase in this apparent Km. When L-palmitoylcarnitine oxidation occurred without ATP accumulation (hexokinase, glucose, ADP, and inorganic phosphate) the apparent Km for the citrate transporter increased two- to threefold. Therefore, the apparent Km for the citrate transporter varied directly with the acid insoluble CoA content. In addition, this Km was increased as a result of beta-oxidation of fatty acids but the mechanism was not solely attributable to a rise in acid insoluble CoA or ATP. The physiological implications of these findings are discussed.
D000818:Animals; D001693:Biological Transport, Active; D002331:Carnitine / Q000494:pharmacology; D002951:Citrates / Q000378:metabolism*; D003065:Coenzyme A / Q000494:pharmacology*; D005227:Fatty Acids / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction; D010169:Palmitic Acids / Q000494:pharmacology*; D051381:Rats
D002951:Citrates; D005227:Fatty Acids; D010169:Palmitic Acids; D002331:Carnitine; D003065:Coenzyme A