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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Abstract

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)2247-2254
Number of pages8
JournalJournal of Lipid Research
Volume48
Issue number10
DOIs
Publication statusPublished - Oct 2007

Keywords

  • biohydrogenation
  • butyrivibrio fibrisolvens
  • clostridium proteoclasticum
  • propionibacterium acnes
  • rumenic acid
  • unsaturated fatty-acids
  • butyrivibrio-fibrisolvens
  • milk-fat
  • lactobacillus-acidophilus
  • cancer-cells
  • dairy-cows
  • fish-oil
  • rumen
  • identification

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