Two-Carbon Compounds and Fatty Acids as Carbon Sources.
Two-Carbon Compounds and Fatty Acids as Carbon Sources.
复制标题
DOI：
10.1128/ecosalplus.3.4.4
复制
发表时间：
2005-11-01
期刊：
影响因子：
--
通讯作者：
Cronan, John E
中科院分区：
文献类型：
--
作者：
Clark, David P;Cronan, John E
本文综述了大肠杆菌和沙门氏菌代谢第一阶段中全部或大部分转化为乙酰辅酶A（CoA）的分子的吸收和降解。这些包括野生型细胞中的乙酸、乙酰乙酸、丁酸和较长的脂肪酸，以及某些突变株中的乙醇和一些较长的醇。作为乙酰辅酶A进入代谢有两个重要的一般后果。首先，从乙酰辅酶A产生能量需要柠檬酸循环和呼吸链两者的操作以氧化所产生的NADH。因此，乙酰辅酶A仅在需氧生长期间或在厌氧呼吸期间与硝酸盐或氧化三甲胺等替代电子受体一起用作能量来源。在没有合适的氧化剂的情况下，乙酰辅酶A通过厌氧发酵途径转化为乙酸和乙醇的混合物。通过柠檬酸循环催化乙酰辅酶A释放乙酰基部分的两个碳原子作为二氧化碳，并且在这些底物上生长作为唯一碳源，因此需要乙醛酸旁路的操作以产生细胞材料。对相关的二碳化合物，乙醇酸和乙醛酸也进行了讨论。然而，尽管有两个碳，这些代谢通过苹果酸和甘油酸，而不是通过乙酰辅酶A。此外，E.能够在乙二醇上生长的大肠杆菌通过乙醇酸途径代谢乙二醇，而不是通过乙酰辅酶A。丙酸代谢也进行了讨论，因为在许多方面，其途径是类似的乙酸。这些途径的转录调控进行了详细讨论。
This review concerns the uptake and degradation of those molecules that are wholly or largely converted to acetyl-coenzyme A (CoA) in the first stage of metabolism in Escherichia coli and Salmonella enterica. These include acetate, acetoacetate, butyrate and longer fatty acids in wild type cells plus ethanol and some longer alcohols in certain mutant strains. Entering metabolism as acetyl-CoA has two important general consequences. First, generation of energy from acetyl-CoA requires operation of both the citric acid cycle and the respiratory chain to oxidize the NADH produced. Hence, acetyl-CoA serves as an energy source only during aerobic growth or during anaerobic respiration with such alternative electron acceptors as nitrate or trimethylamine oxide. In the absence of a suitable oxidant, acetyl-CoA is converted to a mixture of acetic acid and ethanol by the pathways of anaerobic fermentation. Catabolism of acetyl-CoA via the citric acid cycle releases both carbon atoms of the acetyl moiety as carbon dioxide and growth on these substrates as sole carbon source therefore requires the operation of the glyoxylate bypass to generate cell material. The pair of related two-carbon compounds, glycolate and glyoxylate are also discussed. However, despite having two carbons, these are metabolized via malate and glycerate, not via acetyl-CoA. In addition, mutants of E. coli capable of growth on ethylene glycol metabolize it via the glycolate pathway, rather than via acetyl- CoA. Propionate metabolism is also discussed because in many respects its pathway is analogous to that of acetate. The transcriptional regulation of these pathways is discussed in detail.