Program Head of Separation Sciences, Food Protein Research and Development Center, Texas A&M University, College Station, TX 77843, USA.
J Microbiol. 2013 Aug;51(4):471-6. doi: 10.1007/s12275-013-1070-z. Epub 2013 Aug 30.
Conventional beliefs surrounding the linolenic acid (LNA; cis-9 cis-12 cis-15 C18:3) biohydrogenation (BH) pathway propose that it converts to stearic acid (SA) without the formation of conjugated linoleic acid (CLA) as intermediate isomers. However, an advanced study (Lee and Jenkins, 2011) verified that LNA BH yields multiple CLAs. This study utilized the stable isotope tracer to investigate the BH intermediates of (13)C-LNA with different pH conditions (5.5 and 6.5). The (13)C enrichment was calculated as a (13)C/(12)C ratio of labeled minus unlabeled. After 24 h, eight CLA isomers were significantly enriched on both pH treatment, this result verifies that these CLAs originated from (13)C-LNA BH which supports the results of Lee and Jenkins (2011). The enrichment of cis-cis double bond CLAs (cis-9 cis-11 and cis-10 cis-12 CLA) were significantly higher at low pH conditions. Furthermore, the concentration of cis-10 cis-12 CLA at low pH was four times higher than at high pH conditions after a 3 h incubation. These differences support the LNA BH pathways partial switch under different pH conditions, with a strong influence on the cis-cis CLA at low pH. Several mono-, di-, and tri-enoic fatty acid isomers were enriched during 24 h of incubation, but the enrichment was decreased or restricted at low pH treatment. Based on these results, it is proposed that low pH conditions may cause a changed or limited capacity of the isomerization and reduction steps in BH.
传统观念认为，亚麻酸（LNA；顺-9 顺-12 顺-15 C18:3）的生物氢化（BH）途径将其转化为硬脂酸（SA），而没有形成共轭亚油酸（CLA）作为中间异构体。然而，一项深入的研究（Lee 和 Jenkins，2011）证实 LNA BH 会产生多种 CLA。本研究利用稳定同位素示踪剂，在不同 pH 值（5.5 和 6.5）条件下研究（13）C-LNA 的 BH 中间体。（13）C 丰度的计算方法是标记减去未标记的（13）C/（12）C 比值。24 小时后，两种 pH 值处理下均显著富集了八种 CLA 异构体，这一结果证实这些 CLA 源自（13）C-LNA BH，支持 Lee 和 Jenkins（2011）的研究结果。在低 pH 值条件下，顺式顺式双键 CLA（cis-9 cis-11 和 cis-10 cis-12 CLA）的富集程度显著更高。此外，在 3 小时孵育后，低 pH 值条件下 cis-10 cis-12 CLA 的浓度比高 pH 值条件下高四倍。这些差异支持了 LNA BH 途径在不同 pH 值条件下的部分转换，对低 pH 值下的 cis-cis CLA 有强烈影响。在 24 小时孵育过程中，还富集了几种单烯、二烯和三烯脂肪酸异构体，但在低 pH 值处理下，其丰度降低或受到限制。基于这些结果，可以提出低 pH 值条件可能导致 BH 中的异构化和还原步骤的能力发生改变或受限。
