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Photoswitching Behavior of Flavin–Inhibitor Complex in a Nonphotocatalytic Flavoenzyme
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-06-21 , DOI: 10.1021/jacs.2c04763 Bo Zhuang 1 , Marten H Vos 1
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-06-21 , DOI: 10.1021/jacs.2c04763 Bo Zhuang 1 , Marten H Vos 1
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An unprecedented photoswitching phenomenon of flavin–inhibitor complexes in a flavoenzyme was revealed by femtosecond transient absorption spectroscopy. The vast majority of flavoenzymes, including monomeric sarcosine oxidase (MSOX), perform non-light-driven physiological functions. Yet, the participation of flavin cofactors in photoinduced electron transfer reactions is widespread. MSOX catalyzes the oxidative demethylation of sarcosine; methylthioacetate (MTA) is a substrate analog inhibitor that forms a complex with MSOX exhibiting intense absorption bands over the whole visible range due to flavin–MTA charge transfer (CT) interactions. Here, we demonstrate that upon excitation, these CT interactions vanish during a barrierless high quantum yield reaction in ∼300 fs. The initial complex subsequently geminately re-forms in a few nanoseconds near room temperature in a thermally activated way with an activation energy of 28 kJ/mol. We attribute this hitherto undocumented process to a well-defined photoinduced isomerization of MTA in the active site, as corroborated by experiments with the heavier ligand methylselenoacetate. Photoisomerization phenomena involving CT transitions may be further explored in photocatalytic and photoswitching applications of flavoenzymes.
中文翻译：
非光催化黄素酶中黄素抑制剂复合物的光开关行为
飞秒瞬态吸收光谱揭示了黄素酶中黄素抑制剂复合物前所未有的光开关现象。绝大多数黄素酶，包括单体肌氨酸氧化酶 (MSOX)，执行非光驱动的生理功能。然而，黄素辅因子广泛参与光诱导电子转移反应。MSOX催化肌氨酸氧化去甲基化；硫代乙酸甲酯 (MTA) 是一种底物类似物抑制剂，它与 MSOX 形成复合物，由于黄素-MTA 电荷转移 (CT) 相互作用，在整个可见光范围内表现出强烈的吸收带。在这里，我们证明在激发时，这些 CT 相互作用在~300 fs 的无势垒高量子产率反应期间消失。随后，初始复合物以热激活方式在接近室温的几纳秒内重新形成，激活能为 28 kJ/mol。我们将这一迄今未记录的过程归因于活性位点中明确定义的 MTA 光诱导异构化，这一点已通过较重的配体甲基硒乙酸酯的实验得到证实。涉及 CT 转换的光异构化现象可以在黄素酶的光催化和光开关应用中进一步探索。
更新日期：2022-06-21
中文翻译：
非光催化黄素酶中黄素抑制剂复合物的光开关行为
飞秒瞬态吸收光谱揭示了黄素酶中黄素抑制剂复合物前所未有的光开关现象。绝大多数黄素酶，包括单体肌氨酸氧化酶 (MSOX)，执行非光驱动的生理功能。然而，黄素辅因子广泛参与光诱导电子转移反应。MSOX催化肌氨酸氧化去甲基化；硫代乙酸甲酯 (MTA) 是一种底物类似物抑制剂，它与 MSOX 形成复合物，由于黄素-MTA 电荷转移 (CT) 相互作用，在整个可见光范围内表现出强烈的吸收带。在这里，我们证明在激发时，这些 CT 相互作用在~300 fs 的无势垒高量子产率反应期间消失。随后，初始复合物以热激活方式在接近室温的几纳秒内重新形成，激活能为 28 kJ/mol。我们将这一迄今未记录的过程归因于活性位点中明确定义的 MTA 光诱导异构化，这一点已通过较重的配体甲基硒乙酸酯的实验得到证实。涉及 CT 转换的光异构化现象可以在黄素酶的光催化和光开关应用中进一步探索。
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