Biosynthesis of Menaquinone (Vitamin K2) and Ubiquinone (Coenzyme Q).
Biosynthesis of Menaquinone (Vitamin K2) and Ubiquinone (Coenzyme Q).
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DOI：
10.1128/ecosalplus.3.6.3.3
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发表时间：
2009-08
期刊：
影响因子：
--
通讯作者：
Kwon O
中科院分区：
文献类型：
--
作者：
Meganathan R;Kwon O
大肠杆菌和沙门氏菌含有萘醌甲萘醌（MK;维生素K2）和去甲基甲萘醌和苯醌泛醌（辅酶Q; Q）。这两种醌类化合物都来自莽草酸途径，这一途径被称为“多分支代谢树”。“萘醌的生物合成有两种不同的途径。绝大多数原核生物，包括E.大肠杆菌和沙门氏菌，和植物使用邻琥珀酰苯甲酸途径，而少数使用futalosine途径。Q的醌核直接来自分支酸，而MK的醌核通过异分支酸来自分支酸。两种醌的异戊烯基侧链均来自通过2-C-甲基-D-C4-磷酸（非甲羟戊酸）途径形成的异戊烯基二磷酸，甲基来自S-腺苷甲硫氨酸。此外，MK生物合成需要2-酮戊二酸和辅因子ATP、辅酶A和焦磷酸硫胺素。尽管这两种醌类化合物都来源于莽草酸途径，但它们的生物合成存在重要差异。在MK生物合成中，异戊二烯基侧链在倒数第二步引入，伴随着脱羧，而在Q生物合成中，异戊二烯基侧链在第二步引入，保留羧基。在MK生物合成中，直到异戊二烯化的途径的所有反应都是通过可溶性酶进行的，而除了第一种酶之外，参与Q生物合成的所有酶都是膜结合的。在MK生物合成中，最后一步是α C-甲基化;在Q生物合成中，最后一步是α O-甲基化。在Q的生物合成中，第二个C-甲基化和O-甲基化发生在途径的中间部分。尽管Q和MK的生物合成在分支酸上有分歧，但两条途径中的C-甲基化是由相同的甲基转移酶进行的。
Escherichia coliandSalmonellacontain the naphthoquinones menaquinone (MK; vitamin K2) and demethylmenaquinone and the benzoquinone ubiquinone (coenzyme Q; Q). Both quinones are derived from the shikimate pathway, which has been called a "metabolic tree with many branches." There are two different pathways for the biosynthesis of the naphthoquinones. The vast majority of prokaryotes, includingE. coliandSalmonella, and the plants use theo-succinylbenzoate pathway, while a minority uses the futalosine pathway. The quinone nucleus of Q is derived directly from chorismate, while that of MK is derived from chorismate via isochorismate. The prenyl side chains of both quinones are from isopentenyl diphosphate formed by the 2-C-methyl-D-erythritol 4-phosphate (non-mevalonate) pathway and the methyl groups are fromS-adenosylmethionine. In addition, MK biosynthesis requires 2-ketoglutarate and cofactors ATP, coenzyme A, and thiamine pyrophosphate. Despite the fact that both quinones originate from the shikimate pathway, there are important differences in their biosyntheses. The prenyl side chain in MK biosynthesis is introduced at the penultimate step, accompanied by decarboxylation, whereas in Q biosynthesis it is introduced at the second step, with retention of the carboxyl group. In MK biosynthesis, all the reactions of the pathway up to prenylation are carried out by soluble enzymes, whereas all the enzymes involved in Q biosynthesis except the first are membrane bound. In MK biosynthesis, the last step is aC-methylation; in Q biosynthesis, the last step is anO-methylation. In Q biosynthesis a secondC-methylation andO-methylation take place in the middle part of the pathway. Despite the fact that Q and MK biosyntheses diverge at chorismate, theC-methylations in both pathways are carried out by the same methyltransferase.