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 language | English |
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Pages (from-to) | 2247-2254 |
Number of pages | 8 |
Journal | Journal of Lipid Research |
Volume | 48 |
Issue number | 10 |
DOIs | |
Publication status | Published - 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