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首页> 外文期刊>Biochemistry >Superoxide reductase from desulfoarculus baarsii:reaction mechanism and role of glutamate 47 and lysine 48 in catalysis
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Superoxide reductase from desulfoarculus baarsii:reaction mechanism and role of glutamate 47 and lysine 48 in catalysis

机译：巴尔脱硫弧菌的超氧化物还原酶：谷氨酸47和赖氨酸48的反应机理及催化作用

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Superoxide reductase (SOR) is a small metalloenzyme that catalyzes reduction of O2~ to ‘71202 and thus provides an antioxidant mechanism against superoxide radicals. Its active site contains an unusual mononuclear ferrous center, which is very efficient during electron transfer to O2~ [Lombard, M., Fontecave, M., Touati, D., and Nivi~re, V. (2000) J. Biol. Chem. 275, 115—121]. The reaction of the enzyme from Desulfoarculus baarsii with superoxide was studied by pulse radiolysis methods. The first step is an extremely fast bimolecular reaction of superoxide reductase with superoxide, with a rate constant of (1.1 ± 0.3) x i0~ M’ s’. A first intermediate is formed which is converted to a second one at a much slower rate constant of 500 ± 50 sa. Decay of the second intermediate occurs with a rate constant of 25 ± 5 s’. These intermediates are suggested to be iron-superoxide and iron-peroxide species. Furthermore, the role of glutamate 47 and lysine 48, which are the closest charged residues to the vacant sixth iron coordination site, has been investigated by site-directed mutagenesis. Mutation of glutamate 47 into alanine has no effect on the rates of the reaction. On the contrary, mutation of lysine 48 into an isoleucine led to a 20—30-fold decrease of the rate constant of the bimolecular reaction, suggesting that lysine 48 plays an important role during guiding and binding of superoxide to the iron center II. In addition, we report that expression of the lysine 48 sor mutant gene hardly restored to a superoxide dismutase-deficient Escherichia coli mutant the ability to grow under aerobic conditions.
机译：超氧化物还原酶（SOR）是一种小的金属酶，可催化将O2〜还原为‘71202，因此可提供针对超氧化物自由基的抗氧化机制。它的活性位点包含一个不寻常的单核亚铁中心，在电子转移至O2期间非常有效[Lombard，M.，Fontecave，M.，Touati，D.，and Nivire，V.（2000）J.化学275，115—121]。通过脉冲辐射分解方法研究了巴氏脱硫酵母中的酶与超氧化物的反应。第一步是超氧化物还原酶与超氧化物的极快双分子反应，速率常数为（1.1±0.3）x i0〜M's'。形成第一中间体，其以非常慢的500±50 sa的速率常数转化为第二中间体。第二种中间产物的衰减速率常数为25±5 s'。这些中间体被认为是过氧化铁和过氧化铁。此外，已经通过定点诱变研究了谷氨酸47和赖氨酸48的作用，其是最接近空的第六铁配位点的带电荷残基。谷氨酸47突变为丙氨酸对反应速率没有影响。相反，赖氨酸48突变为异亮氨酸导致双分子反应速率常数降低20-30倍，这表明赖氨酸48在超氧化物与铁中心II的结合和引导中起着重要作用。此外，我们报告说，赖氨酸48 sor突变基因的表达很难恢复到超氧化物歧化酶缺陷型大肠杆菌突变体在有氧条件下生长的能力。

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