Brackmann R, Fuchs G
Angewandte Mikrobiologie, Universität Ulm, Germany.
Eur J Biochem. 1993 Apr 1;213(1):563-71. doi: 10.1111/j.1432-1033.1993.tb17795.x.
The reductive removal of aromatic hydroxyl functions plays an important role in the anaerobic metabolism of many phenolic compounds. We describe a new enzyme from a denitrifying Pseudomonas sp., 4-hydroxybenzoyl-CoA reductase (dehydroxylating), which reductively dehydroxylates 4-hydroxybenzoyl-CoA to benzoyl-CoA. The enzyme plays a role in the anaerobic degradation of phenol, 4-hydroxybenzoate, p-cresol, 4-hydroxyphenylacetate, and other aromatic compounds of which 4-hydroxybenzoyl-CoA is an intermediate. The enzyme is therefore induced only under anoxic conditions with these aromatic substrates, but not with benzoate or under aerobic conditions. A similar enzyme which reductively dehydroxylates 3-hydroxybenzoyl-CoA is induced during anaerobic growth with 3-hydroxybenzoate. The soluble enzyme 4-hydroxybenzoyl-CoA reductase was purified. It has a molecular mass of 260 kDa and consists of three subunits of 75, 35, and 17 kDa. The subunit composition is likely to be a2b2c2. The enzyme contains 12 mol iron/mol and 12 mol acid-labile sulfur/mol and exhibits a typical ultraviolet/visible spectrum of an iron-sulfur protein. The reaction requires a reduced electron donor such as reduced viologen dyes; no other co-catalysts are required, the product is benzoyl-CoA and oxidized dye. The reductase is rapidly inactivated by oxygen. The inactivation by low concentrations of cyanide or azide in a pseudo-first-order time course suggests that it may contain a transition metal in an oxidation state which reacts with these ligands. 4-Hydroxybenzoyl-CoA reductase represents a type of enzyme which is common in anaerobic aromatic metabolism of phenolic compounds. A similar enzyme is demonstrated in Rhodopseudomonas palustris anaerobically grown with 4-hydroxybenzoate. The biological significance of reductive dehydroxylation of aromatics and a possible reaction mechanism similar to the Birch reduction are discussed.
芳香族羟基官能团的还原去除在许多酚类化合物的厌氧代谢中起着重要作用。我们描述了一种来自反硝化假单胞菌属的新酶，4-羟基苯甲酰辅酶A还原酶（脱羟基），它将4-羟基苯甲酰辅酶A还原脱羟基生成苯甲酰辅酶A。该酶在苯酚、4-羟基苯甲酸、对甲酚、4-羟基苯乙酸以及其他以4-羟基苯甲酰辅酶A为中间体的芳香族化合物的厌氧降解中起作用。因此，该酶仅在以这些芳香族底物为条件的缺氧环境下被诱导，而在以苯甲酸盐为底物或有氧条件下则不会被诱导。一种类似的将3-羟基苯甲酰辅酶A还原脱羟基的酶在以3-羟基苯甲酸进行厌氧生长时被诱导。可溶性酶4-羟基苯甲酰辅酶A还原酶被纯化。它的分子量为260 kDa，由75 kDa、35 kDa和17 kDa的三个亚基组成。亚基组成可能是a2b2c2。该酶每摩尔含有12摩尔铁和12摩尔酸不稳定硫，并呈现出典型的铁硫蛋白紫外/可见光谱。该反应需要一种还原型电子供体，如还原型紫精染料；不需要其他共催化剂，产物是苯甲酰辅酶A和氧化型染料。该还原酶会被氧气迅速灭活。在假一级反应时间进程中，低浓度的氰化物或叠氮化物使其失活，这表明它可能含有一种处于与这些配体反应的氧化态的过渡金属。4-羟基苯甲酰辅酶A还原酶代表了一种在酚类化合物的厌氧芳香族代谢中常见的酶类型。在以4-羟基苯甲酸进行厌氧生长的沼泽红假单胞菌中也证明了一种类似的酶。本文讨论了芳香族化合物还原脱羟基的生物学意义以及一种类似于Birch还原的可能反应机制。
