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首页> 外文期刊>Biochemistry >Quinone reductase reaction catalyzed by Streptococcus faecalis NADH peroxidase.
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Quinone reductase reaction catalyzed by Streptococcus faecalis NADH peroxidase.

机译：粪链球菌NADH过氧化物酶催化醌还原酶反应。

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摘要

NADH peroxidase is a flavoenzyme having a single redox-active thiol, Cys42, that cycles between sulfenate and thiol forms in the NADH-dependent reduction of hydrogen peroxide. NADH peroxidase catalyzes the NADH-dependent reduction of quinones with turnover numbers between 1.2 and 3.9 s-1, per mole of FAD, at pH 7.5. The bimolecular rate constants for quinone reduction, V/K, ranged from 4.3 x 10(3) to 6.0 x 10(5) M-1 s-1 for 14 quinones whose redox potentials varied between -0.41 and 0.09 V. The logarithms of the V/K values for these quinones are hyperbolically dependent on their single-electron reduction potentials (E7(1). One-electron reduction of benzoquinone accounts for about 50% of the total electron transfer catalyzed by NADH peroxidase at pH 7, with the remainder of the reduction being catalyzed by a two-electron (hydride) transfer. Cys42 can be irreversibly oxidized to the sulfonate by hydrogen peroxide, with inactivation of the peroxidatic activity of the enzyme. The residual quinone reductaseactivity of NADH peroxidase which has undergone oxidative inactivation of the active site Cys42 indicates that this residue is not involved in the reduction of the quinones. Product inhibition studies suggest the possibility of overlap of the pyridine nucleotide and quinone binding sites in the reduced enzyme at low pH values. The pH dependence of the maximum velocity of naphthoquinone reduction shows that deprotonation of an enzymic group, exhibiting a pK value of ca. 6.2, decreases the maximal velocity. Primary deuterium kinetic isotope effects on V and V/K for quinone-dependent NADH oxidation increase upon protonation of a group, exhibiting a pK value of 6.4.(ABSTRACT TRUNCATED AT 250 WORDS)
机译：NADH过氧化物酶是一种具有单一氧化还原活性硫醇Cys42的黄素酶，在依赖NADH的过氧化氢还原反应中，亚硫酸盐和硫醇之间形成循环。 NADH过氧化物酶可催化NADH依赖的醌还原，在pH 7.5下，每摩尔FAD的转换数在1.2到3.9 s-1之间。醌还原的双分子速率常数V / K，对于氧化还原电位在-0.41至0.09 V之间变化的14个醌，范围为4.3 x 10（3）至6.0 x 10（5）M-1 s-1。这些醌的V / K值双曲线取决于其单电子还原电势（E7（1）。在pH 7时，NADH过氧化物酶催化的苯醌的单电子还原约占总电子转移的50％。其余的还原反应是由两电子（氢化物）转移催化的，Cys42可以被过氧化氢不可逆地氧化成磺酸盐，同时使该酶的过氧化活性失活; NADH过氧化物酶的残留醌还原酶活性已经被氧化失活。活性位点Cys42的突变表明该残基不参与醌的还原，产物抑制研究表明，在还原反应中吡啶核苷酸和醌结合位点可能重叠在低pH值时会产生酶。 pH值取决于萘醌最大还原速度，表明酶基团去质子化，pK值为ca。 6.2，降低最大速度。一组质子化后，醌依赖的NADH氧化对V和V / K的主要氘动力学同位素影响，pK值为6.4（摘要截短为250字）

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