The electron transport chain in anaerobically functioning eukaryotes
The electron transport chain in anaerobically functioning eukaryotes
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DOI：
10.1016/s0005-2728(98)00045-0
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发表时间：
1998-06-10
影响因子：
4.3
通讯作者：
Van Hellemond, JJ
中科院分区：
文献类型：
--
作者：
Tielens, AGM;Van Hellemond, JJ
许多低等真核生物可以通过发酵途径在厌氧条件下存活，该发酵途径涉及使用内源产生的富马酸盐的还原作为电子汇。富马酸盐的还原与电子传递有关，电子传递是在一个特别适应的、厌氧的电子传递链中进行的。具有克雷布斯循环活性的有氧能量代谢伴随着电子从琥珀酸通过呼吸链的复合物II转移到泛醌。另一方面，在厌氧代谢中，富马酸盐作为末端电子受体，电子从玫瑰醌转移到富马酸盐，这是相反的方向。泛醌在体内不能代替玫瑰醌还原富马酸，因为泛醌只能接受来自络合物II的电子，而不能将它们提供给富马酸。Rhodoquinone的氧化还原电位比泛醌低，能够为富马酸提供电子。真核生物中的延胡索酸还原酶与苯醌相互作用，而大多数原核生物中的延胡索酸还原酶与萘醌、甲基萘醌和去甲基甲基萘醌相互作用。延胡索酸还原酶是许多真核生物厌氧功能所必需的酶，其结构与琥珀酸脱氢酶非常相似，后者是催化逆反应的克雷布斯循环酶。在原核生物中，这些酶根据外部条件差异表达。现在出现的证据表明，在真核生物中也存在两种不同的酶，用于琥珀酸氧化和富马酸还原，其差异表达。(C)1998年Elsevier Science B.V.
Many lower eukaryotes can survive anaerobic conditions via a fermentation pathway that involves the use of the reduction of endogenously produced fumarate as electron sink. This fumarate reduction is linked to electron transport in an especially adapted, anaerobically functioning electron-transport chain.An aerobic energy metabolism with Krebs cycle activity is accompanied by electron transfer from succinate to ubiquinone via complex II of the respiratory chain. On the other hand, in an anaerobic metabolism, where fumarate functions as terminal electron acceptor, electrons are transferred from rhodoquinone to fumarate, which is the reversed direction. Ubiquinone cannot replace rhodoquinone in the process of fumarate reduction in vivo, as ubiquinone can only accept electrons from complex II and cannot donate them to fumarate. Rhodoquinone, with its lower redox potential than ubiquinone, is capable of donating electrons to fumarate. Eukaryotic fumarate reductases were shown to interact with rhodoquinone (a benzoquinone), whereas most prokaryotic fumarate reductases interact with the naphtoquinones menaquinone and demethylmenaquinone.Fumarate reductase, the enzyme essential for the anaerobic functioning of many eukaryotes, is structurally very similar to succinate dehydrogenase, the Krebs cycle enzyme catalysing the reverse reaction. In prokaryotes these enzymes are differentially expressed depending on the external conditions. Evidence is now emerging that also in eukaryotes two different enzymes exist for succinate oxidation and fumarate reduction that are differentially expressed. (C) 1998 Elsevier Science B.V.