Biogenesis of dicarboxylic acids in rat liver homogenate studied by 13C labeling.
The aim of this investigation is to assess whether long-chain fatty acids can be a substrate for omega-oxidation and the subsequent beta-oxidation to produce medium-chain dicarboxylic acids normally found in urine. Isolated rat liver 10,000 g supernatant and pellet fractions were used as the source of enzymes. The metabolism of palmitate was studied using [1,2,3,4-13C4]hexadecanoic acid as tracer. Selected ion monitoring mass spectrometry was utilized for the determination of isotope enrichments in precursor and products. Palmitate was found to be a good substrate for omega-oxidation; the rate was only slightly slower than decanoate. The beta-oxidation of [1,2,3,4-13C4]hexadecanedioic acid yielded labeled adipic, suberic, and sebacic acids. Isotope distribution in these dicarboxylic acids consisted mostly of unlabeled molecules (M + 0) and molecules labeled with four 13C (M + 4), in agreement with a beta-oxidation initiated equally from both carboxyl ends of the precursor. Significant enrichments (1-8%) with only two 13C labels (M + 2) indicate a partial bidirectional beta-oxidation. The direct metabolic conversion of hexadecanedioate to succinate was documented by the significant enrichment (1.40-1.90%) in M + 4 of succinate. These data indicate that long-chain fatty acids can be a substrate for the production of medium-chain dicarboxylates and the eventual direct conversion to succinate.
Jin
S J
SJ
Medical Research Service, Veterans Affairs Medical Center, Cleveland, Ohio.
Tserng
K Y
KY
D000818:Animals; D002021:Buffers; D002247:Carbon Isotopes; D002264:Carboxylic Acids / Q000378:metabolism; D002952:Citric Acid Cycle; D003998:Dicarboxylic Acids / Q000378:metabolism*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006885:Hydroxybutyrates / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism; D010084:Oxidation-Reduction; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014233:Tricarboxylic Acids / Q000378:metabolism
D002021:Buffers; D002247:Carbon Isotopes; D002264:Carboxylic Acids; D003998:Dicarboxylic Acids; D006885:Hydroxybutyrates; D010169:Palmitic Acids; D010710:Phosphates; D014233:Tricarboxylic Acids; D019308:Palmitic Acid