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首页> 外文期刊>Applied Microbiology >Importance of the Isovalerate Carboxylation Pathway of Leucine Biosynthesis in the Rumen
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Importance of the Isovalerate Carboxylation Pathway of Leucine Biosynthesis in the Rumen

机译：瘤胃中亮氨酸生物合成的等价羧化途径的重要性

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Certain anaerobic ruminal bacteria synthesize the leucine carbon skeleton by use of a pathway different from that described in other microorganisms. These organisms carboxylate the intact carbon skeleton of isovalerate, synthesizing leucine-2-C14 from isovalerate-1-C14. Strains of Bacteroides ruminicola and Peptostreptococcus elsdenii were like Ruminococcus flavefaciens in that they incorporated appreciable amounts of C14 from isovalerate-1-C14 into cellular protein and in that the only labeled amino acid found was leucine. The specific activity of β-isopropylmalate dehydrogenase in extracts from R. flavefaciens and from the mixed bacterial population from the rumen was very low as compared with the specific activity of this enzyme in extracts from Escherichia coli. This suggests that the pathway of leucine biosynthesis that operates in many aerobic and facultative microorganisms is not the major pathway in rumen bacteria. This was supported by the finding that after fermentation of whole rumen contents with acetate-2-C14, leucine from the bacterial cells had a specific activity lower than one would expect if acetate was incorporated directly into carbons 1 and 2 of leucine.
机译：某些厌氧瘤胃细菌利用不同于其他微生物中描述的途径来合成亮氨酸碳骨架。这些生物将异戊酸的完整碳骨架羧基化，从异戊酸-1-C14合成亮氨酸-2-C14。拟杆菌（Bacteroides ruminicola）和拟肽链球菌（Peptostreptococcus elsdenii）的菌株类似于黄褐球菌，因为它们将相当量的来自异戊酸-1-C14的C14掺入了细胞蛋白中，并且发现的唯一标记氨基酸是亮氨酸。与黄曲霉的提取物和瘤胃的混合细菌群体的提取物中的β-异丙基苹果酸脱氢酶的比活性相比，大肠杆菌提取物中的β-异丙基苹果酸脱氢酶的比活性非常低。这表明在许多好氧和兼性微生物中起作用的亮氨酸生物合成途径不是瘤胃细菌的主要途径。这得到以下发现的支持：在用乙酸盐-2-C14发酵整个瘤胃内容物后，来自细菌细胞的亮氨酸的比活性低于将乙酸盐直接掺入亮氨酸的碳1和2中所期望的比活性。

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