Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, CA, United States.
Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, CA, United States.
Bioelectrochemistry. 2021 Feb;137:107679. doi: 10.1016/j.bioelechem.2020.107679. Epub 2020 Oct 13.
Styrene monooxygenase (SMO) is a two-component flavoenzyme composed of NADH-dependent flavin reductase (SMOB) and FAD-specific styrene epoxidase (NSMOA) components. The enantioselective styrene epoxidation reaction catalyzed by this enzyme can be streamlined for chemosynthetic applications by substituting NADH and the reductase with an electrode to supply the epoxidase with reducing equivalents required for catalysis. Slow kinetics of adsorption and desorption of FAD from the electrode surface and unproductive side reactions of the reduced flavin with oxygen limit the efficiency of direct electroenzymatic catalysis. In the present work we develop a miniature spectroelectrochemical cell equipped with a copper electrode for the anodic synthesis of Cu(I) chelates of EDTA, glutamate, and citrate as FAD-reducing agents, and a platinum electrode for the electrolytic generation of oxygen. Copper oxidized in the flavin reduction reaction can be reclaimed subsequently as copper metal at the electrode surface. About 80% transformation of styrene is achieved in a single cell cycle of reduction and oxygenation at pH 7 and 25 °C in good agreement with that predicted by numerical simulation. When the cell is operated in two successive cycles, styrene oxide can be synthesized with an electroenzymatic epoxidation activity of 663U/g in 94% yield. This approach to electroenzymatic catalysis shows promise for the quantitative transformation of styrene to styrene oxide and may be applied more generally to other flavoprotein monooxygenases.
苯乙烯单加氧酶（SMO）是一种由 NADH 依赖性黄素还原酶（SMOB）和 FAD 特异性苯乙烯环氧化酶（NSMOA）组成的双组分黄素酶。该酶催化的对映选择性苯乙烯环氧化反应可以通过用电极替代 NADH 和还原酶来为环氧化酶提供催化所需的还原当量，从而实现化学合成应用的简化。FAD 从电极表面的吸附和解吸动力学缓慢以及还原黄素与氧气的非生产性副反应限制了直接电酶催化的效率。在本工作中，我们开发了一种带有铜电极的微型光谱电化学池，用于阳极合成 EDTA、谷氨酸和柠檬酸盐的 Cu(I) 配合物作为 FAD 还原剂，以及带有铂电极的用于氧气电解产生的池。在黄素还原反应中氧化的铜可以随后在电极表面作为铜金属回收。在 pH 7 和 25°C 的单个还原和氧化细胞循环中，实现了约 80%的苯乙烯转化，与数值模拟预测的结果非常吻合。当该细胞在两个连续的循环中运行时，可以以 663U/g 的电酶氧化活性在 94%的收率下合成苯乙烯氧化物。这种电酶催化方法有望实现苯乙烯向苯乙烯氧化物的定量转化，并且可能更普遍地应用于其他黄素蛋白单加氧酶。
