title: Evidence for intermediate channeling in mitochondrial beta-oxidation.
abstract: The accumulation of beta-oxidation intermediates was studied by incubating normal and beta-oxidation enzyme-deficient human fibroblasts with [2H4]linoleate and L-carnitine and analyzing the resultant acylcarnitines by tandem mass spectrometry. Labeled decenoyl-, octanoyl-, hexanoyl-, and butyrylcarnitines were the only intermediates observed with normal cells. Intermediates of longer chain length, corresponding to substrates for the beta-oxidation enzymes associated with the inner mitochondrial membrane, were not observed unless a cell line was deficient in one of these enzymes, such as very-long-chain acyl-CoA dehydrogenase, long-chain 3-hydroxyacyl-CoA dehydrogenase, or electron transfer flavoprotein dehydrogenase. Matrix enzyme deficiencies, such as medium- and short-chain acyl-CoA dehydrogenases, were characterized by elevated concentrations of intermediates corresponding to their respective substrates (octanoyl- and decenoylcarnitines in medium-chain acyl-CoA dehydrogenase deficiency and butyrylcarnitine in short-chain acyl-CoA dehydrogenase deficiency). These observations agree with the notion of intermediate channeling due to the organization of beta-oxidation enzymes in complexes. The only exception is the incomplete channeling from thiolase to acyl-CoA dehydrogenase in the matrix. This situation may be a consequence of only one 3-ketoacyl-CoA thiolase being unable to interact with the several acyl-CoA dehydrogenases in the matrix.
authors: Department of Pediatrics, Duke University Medical Center, Research Triangle Park, North Carolina 27709.
authors: M A
authors: MA
authors: Nada
authors: W J
authors: WJ
authors: Rhead
authors: H
authors: H
authors: Sprecher
authors: H
authors: H
authors: Schulz
authors: C R
authors: CR
authors: Roe
mesh_terms: D042964:Acyl-CoA Dehydrogenase; D044942:Acyl-CoA Dehydrogenase, Long-Chain; D002478:Cells, Cultured; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism
chemical_list: D008041:Linoleic Acids; D010169:Palmitic Acids; D019308:Palmitic Acid; D019787:Linoleic Acid; D042964:Acyl-CoA Dehydrogenase; D044942:Acyl-CoA Dehydrogenase, Long-Chain