Enzymatic reductions in the anaerobic aromatic at extremely low redox potentials

近年来，在厌氧菌的芳香代谢过程中发现了许多前所未有的酶促反应。这种代谢的两个关键酶，苯甲酰辅酶a还原酶（BCR，去芳化）和4-羟基苯甲酰辅酶a还原酶（HCR，去羟化），在极低的氧化还原电位下催化独特的还原，其机制类似于有机合成中的桦木还原。BCR通过将苯甲酰辅酶a的还原脱芳化与atp的化学计量水解相结合，克服了高氧化还原屏障。相反，由HCR催化的酶促去羟基化反应不耦合于一个出能反应。BCR包含三个[4Fe-4S]簇，其中一个应该与二硫化物有特殊的配位。HCR是一种黄嘌呤氧化酶家族的铁- s /黄/钼蛋白。两种酶的结构/功能关系将通过蛋白质结晶/- x射线分析和一些光谱技术来阐明。BCR和HCR将在不同的兼性和严格厌氧细菌中降解芳香族化合物。所获得的结果应该为极低电位下酶氧化还原过程的机制提供一般的见解。

In recent years, a number of unprecedented enzymatic reactions have been discovered in the aromatic metabolism of anaerobic bacteria. Two key enzymes of this metabolism, benzoyl-CoA reductase (BCR, dearomatizing) and 4-hydroxybenzoyl-CoA reductase (HCR, dehydroxylating), catalyze unique reductions at extremely low redox potentials in mechanisms similar to the Birch reduction in organic synthesis. BCR overcomes the high redox barrier by coupling the reductive dearomatization of benzoyl-CoA to a stoichiometrical ATP-hydrolysis. In contrast, the enzymatic dehydroxylation catalyzed by HCR is not coupled to an exergonic reaction. BCR contains three [4Fe-4S] clusters, one of which is supposed to be in special coordination with a disulfide species. HCR is an Fe-S/flavo/molybdo-protein belonging to the xanthine oxidase family. Structure/function relationships of both enzymes will be elucidated by protein crystallization/- X-Ray analysis and by a number of spectroscopic techniques. BCR and HCR will be studied in different facultative and strictly anaerobic bacteria degrading aromatic compounds. The results obtained should provide general insights into the mechanism of enzymatic redox processes at extremely low potentials.