AJP - Endocrinology and Metabolism, Vol 261, Issue 6 E719-E724, Copyright © 1991 by American Physiological Society
Biogenesis of dicarboxylic acids in rat liver homogenate studied by 13C labeling
S. J. Jin and K. Y. Tserng
Medical Research Service, Veterans Affairs Medical Center, Cleveland, Ohio.
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.
