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首页> 外文期刊>Journal of bacteriology >The Apparent Malate Synthase Activity of Rhodobacter sphaeroides Is Due to Two Paralogous Enzymes, (3S)-Malyl-Coenzyme A (CoA)/β-Methylmalyl-CoA Lyase and (3S)- Malyl-CoA Thioesterase
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The Apparent Malate Synthase Activity of Rhodobacter sphaeroides Is Due to Two Paralogous Enzymes, (3S)-Malyl-Coenzyme A (CoA)/β-Methylmalyl-CoA Lyase and (3S)- Malyl-CoA Thioesterase

机译：球形球形红细菌的表观苹果酸合酶活性是由于两种同源的酶，（3S）-苹果酰辅酶A（CoA）/β-甲基苹果酰-CoA裂解酶和（3S）-苹果酰-CoA硫酯酶

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Assimilation of acetyl coenzyme A (acetyl-CoA) is an essential process in many bacteria that proceeds via the glyoxylate cycle or the ethylmalonyl-CoA pathway. In both assimilation strategies, one of the final products is malate that is formed by the condensation of acetyl-CoA with glyoxylate. In the glyoxylate cycle this reaction is catalyzed by malate synthase, whereas in the ethylmalonyl-CoA pathway the reaction is separated into two proteins: malyl-CoA lyase, a well-known enzyme catalyzing the Claisen condensation of acetyl-CoA with glyoxylate and yielding malyl-CoA, and an unidentified malyl-CoA thioesterase that hydrolyzes malyl-CoA into malate and CoA. In this study the roles of Mcl1 and Mcl2, two malyl-CoA lyase homologs in Rhodobacter sphaeroides, were investigated by gene inactivation and biochemical studies. Mcl1 is a true (3S)-malyl-CoA lyase operating in the ethylmalonyl-CoA pathway. Notably, Mcl1 is a promiscuous enzyme and catalyzes not only the condensation of acetyl-CoA and glyoxylate but also the cleavage of β-methylmalyl-CoA into glyoxylate and propionyl-CoA during acetyl-CoA assimilation. In contrast, Mcl2 was shown to be the sought (3S)-malyl-CoA thioesterase in the ethylmalonyl-CoA pathway, which specifically hydrolyzes (3S)-malyl-CoA but does not use β-methylmalyl-CoA or catalyze a lyase or condensation reaction. The identification of Mcl2 as thioesterase extends the enzyme functions of malyl-CoA lyase homologs that have been known only as “Claisen condensation” enzymes so far. Mcl1 and Mcl2 are both related to malate synthase, an enzyme which catalyzes both a Claisen condensation and thioester hydrolysis reaction.
机译：乙酰辅酶A（乙酰辅酶A）的同化是许多细菌中必不可少的过程，这些过程是通过乙醛酸循环或乙基丙二酰辅酶A途径进行的。在两种同化策略中，最终产物之一是苹果酸，它是由乙酰辅酶A与乙醛酸酯缩合形成的。在乙醛酸循环中，该反应由苹果酸合酶催化，而在乙基丙二酰-CoA途径中，该反应分为两种蛋白质：丙二酰-CoA裂解酶，一种众所周知的酶，其催化乙酰辅酶A与乙醛酸的克莱森缩合并生成丙二酸。 -CoA，以及一种未知的malyl-CoA硫酯酶，可将malyl-CoA水解为苹果酸和CoA。通过基因灭活和生化研究，研究了球形芽孢杆菌（Rhodobacter sphaeroides）中两个Malyl-CoA裂解酶同系物Mcl1和Mcl2的作用。 Mcl1是在乙基丙二酰辅酶A途径中运作的真正的（3 S ）-丙二酰辅酶A裂解酶。值得注意的是，Mcl1是一种混杂酶，不仅在乙酰辅酶A同化过程中催化乙酰辅酶A和乙醛酸酯的缩合，而且还催化β-甲基丙二酰辅酶A裂解为乙醛酸酯和丙酰辅酶A。相比之下，Mcl2被证明是乙基丙二酰-CoA途径中寻求的（3 S ）-丙二酰-CoA硫酯酶，可特异性水解（3 S ）-丙二酸- CoA，但不使用β-甲基苹果基-CoA或催化裂解酶或缩合反应。将Mcl2鉴定为硫酯酶可扩展Malyl-CoA裂解酶同系物的酶功能，迄今为止仅被称为“克莱森缩合”酶。 Mcl1和Mcl2都与苹果酸合酶有关，苹果酸合酶既催化克莱森缩合反应，又催化硫酯水解反应。

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