Studies on the transport of acetyl groups from peroxisomes to mitochondria in isolated liver cells oxidizing the polyunsaturated fatty acid 22:4n-6.
The oxidation of the fatty acid [1-(14)C]22:4n-6 was studied in isolated hepatocytes. Labeled acetate was the main acid soluble product identified by HPLC after short incubation periods. At low substrate concentrations and longer incubations [(14)C]acetate was gradually replaced by labeled beta-hydroxybutyrate, acetoacetate and oxaloacetate/malate. Preincubation with 2-tetradecylglycidic acid (TDGA), an inhibitor of mitochondrial fatty acid oxidation, did not reduce the oxidation but acetate was the only product recovered. TDGA also strongly inhibited the metabolism of added [1-(14)C]acetate to mitochondrial oxidation products. During the preparation procedure of hepatocytes the cellular L-carnitine concentration was decreased but it was restored after preincubation with L-carnitine. With low [1-(14)C]22:4n-6, concentrating a low level of [(14)C]acetate and high levels of labeled mitochondrial oxidation products were recovered after preincubation with L-carnitine. A small amount of [(14)C]acetylcarnitine was also detected under this incubation condition. The results suggest that a significant part of labeled acetyl groups from the peroxisomal oxidation of [1-(14)C]22:4n-6 is transported to the mitochondria as free acetate. Moreover, the results also suggest that L-carnitine at physiological concentrations may facilitate the transport of part of the acetyl groups from peroxisomes to mitochondria as acetylcarnitine. However, the possibility that an increased cellular L-carnitine concentration may stimulate oxidation of [1-(14)C]22:4n-6 in mitochondria could not be excluded.
Tran
T N
TN
Institute of Clinical Biochemistry, National Hospital, University of Oslo, NO-0027, Oslo, Norway. t.n.tran@labmed.uio.no
Christophersen
B O
BO
D000085:Acetates / Q000032:analysis / Q000378:metabolism; D000105:Acetyl Coenzyme A / Q000032:analysis / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002245:Carbon Dioxide / Q000032:analysis; D002250:Carbon Radioisotopes; D002331:Carnitine / Q000494:pharmacology; D002478:Cells, Cultured; D004852:Epoxy Compounds / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism; D020675:Peroxisomes / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000085:Acetates; D002250:Carbon Radioisotopes; D004852:Epoxy Compounds; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D002245:Carbon Dioxide; D019308:Palmitic Acid; D000105:Acetyl Coenzyme A; C026219:docosapentaenoic acid; C021756:2-tetradecylglycidic acid; D002331:Carnitine