...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Biochemistry >Nature of the Reaction Intermediates in the Flavin Adenine Dinucleotide-Dependent Epoxidation Mechanism of Styrene Monooxygenase
【24h】

Nature of the Reaction Intermediates in the Flavin Adenine Dinucleotide-Dependent Epoxidation Mechanism of Styrene Monooxygenase

机译：苯乙烯单加氧酶的黄素腺嘌呤二核苷酸依赖性环氧化机理中反应中间体的性质

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Styrene monooxygenase (SMO) is a two-component flavoenzyme composed of an NADH-specific flavin reductase (SMOB) and FAD-specific styrene epoxidase (NSMOA). NSMOA binds tightly to reduced FAD and catalyzes the stereospecific addition of one atom of molecular oxygen to the vinyl side chain of styrene in the enantioselective synthesis of S-styrene oxide. In this mechanism, molecular oxygen first reacts with NSMOA(FAD_(red)) to yield an FAD C(4a)-peroxide intermediate. This species is nonfluorescent and has an absorbance maximum of 382 nm. Styrene then reacts with the peroxide intermediate with a second-order rate constant of (2.6 ±- 0.1) x 10~6 M~(-1) s~(-1) to yield a fluorescent intermediate with an absorbance maximum of 368 nm. We compute an activation free energy of 8.7 kcal/mol for the oxygenation step, in good agreement with that expected for a peroxide-catalyzed epoxidation, and acid-quenched samples recovered at defined time points in the single-turnover reaction indicate that styrene oxide synthesis is coincident with the formation phase of the fluorescent intermediate. These findings support FAD C(4a)-peroxide being the oxygen atom donor and the identity of the fluorescent intermediate as an FAD C(4a)-hydroxide product of the styrene epoxidation. Overall, four pH-dependent rate constants corresponding to peroxyflavin formation (pk_a = 7.2), styrene epoxidation (pK_a = 7.7), styrene oxide dissociation (pK_a = 8.3), and hydroxyflavin dehydration (pK_a = 7.6) are needed to fit the single-turnover kinetics.
机译：苯乙烯单加氧酶（SMO）是由NADH特异性黄素还原酶（SMOB）和FAD特异性苯乙烯环氧酶（NSMOA）组成的两组分黄素酶。 NSMOA与还原的FAD紧密结合，并在S-氧化苯乙烯的对映选择性合成中，将一个分子氧原子立体定向加成到苯乙烯的乙烯基侧链上。在这种机制下，分子氧首先与NSMOA（FAD_（red））反应生成FAD C（4a）-过氧化物中间体。该物质是非荧光物质，最大吸收值为382 nm。苯乙烯然后以（2.6±-0.1）x 10〜6 M〜（-1）s〜（-1）的二级速率常数与过氧化物中间体反应，生成最大吸光度为368 nm的荧光中间体。我们计算出氧合步骤的活化自由能为8.7 kcal / mol，与过氧化物催化的环氧化的预期相符，并且在单周转反应的指定时间点回收的酸猝灭样品表明，苯乙烯氧化物的合成与荧光中间体的形成阶段一致。这些发现支持FAD C（4a）-过氧化物是氧原子供体，并且荧光中间体鉴定为苯乙烯环氧化的FAD C（4a）-氢氧化物产物。总的来说，需要四个与pH有关的速率常数，分别与过氧黄素形成（pk_a = 7.2），苯乙烯环氧化（pK_a = 7.7），苯乙烯氧化物的解离（pK_a = 8.3）和羟基黄素脱水（pK_a = 7.6）相适应。周转动力学。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号