Isomers of conjugated linoleic acids are synthesized via different mechanisms in ruminal digesta and bacteria

R John Wallace, Nest McKain, Kevin J Shingfield, Estelle Devillard

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148 Citations (SciVal)


Digesta samples from the ovine rumen and pure ruminal bacteria were incubated with linoleic acid (LA) in deuterium oxide-containing buffer to investigate the mechanisms of the formation of conjugated linoleic acids (CLAs). Rumenic acid (RA; cis-9,trans-11-18:2), trans-9,trans-11-18:2, and trans-10,cis-12-18:2 were the major CLA intermediates formed from LA in ruminal digesta, with traces of trans-9,cis-11-18:2, cis-9,cis-11-18:2, and cis-10,cis-12-18:2. Mass spectrometry indicated an increase in the n+1 isotopomers of RA and other 9,11-CLA isomers, as a result of labeling at C-13, whereas 10,12 isomers contained minimal enrichment. In pure culture, Butyrivibrio fibrisolvens and Clostridium proteoclasticum produced mostly RA with minor amounts of other 9,11 isomers, all labeled at C-13. Increasing the deuterium enrichment in water led to an isotope effect, whereby (1)H was incorporated in preference to (2)H. In contrast, the type strain and a ruminal isolate of Propionibacterium acnes produced trans-10,cis-12-18:2 and other 10,12 isomers that were minimally labeled. Incubations with ruminal digesta provided no support for ricinoleic acid (12-OH,cis-9-18:1) as an intermediate of RA synthesis. We conclude that geometric isomers of 10,12-CLA are synthesized by a mechanism that differs from the synthesis of 9,11 isomers, the latter possibly initiated by hydrogen abstraction on C-11 catalyzed by a radical intermediate enzyme.
Original languageEnglish
Pages (from-to)2247-54
Number of pages8
JournalJournal of Lipid Research
Issue number10
Publication statusPublished - Oct 2007


  • Animals
  • Bacteria
  • Deuterium Oxide
  • Fatty Acids
  • Gastrointestinal Tract
  • Isomerism
  • Linoleic Acid
  • Linoleic Acids
  • Linoleic Acids, Conjugated
  • Models, Biological
  • Protein Isoforms
  • Ruminants
  • Sheep
  • Time Factors


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