Department of Chemistry, University of Louisville, Louisville, KY, United States.
Department of Chemistry, University of Louisville, Louisville, KY, United States.
Vitam Horm. 2022;119:185-220. doi: 10.1016/bs.vh.2022.01.012. Epub 2022 Mar 3.
The biologically active vitamin B derivates, methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are ubiquitous organometallic cofactors. In addition to their key roles in enzymatic catalysis, B cofactors have complex photolytic properties which have been the target of experimental and theoretical studies. With the recent discovery of B-dependent photoreceptors, there is an increased need to elucidate the underlying photochemical mechanisms of these systems. This book chapter summarizes the photolytic properties of MeCbl- and AdoCbl-dependent enzymes with particular emphasis on the effect of the environment of the cofactor on the excited state processes. These systems include isolated MeCbl and AdoCbl as well as the enzymes, ethanolamine ammonia-lyase (EAL), glutamate mutase (GLM), methionine synthase (MetH), and photoreceptor CarH. Central to determining the photodissociation mechanism of each system is the analysis of the lowest singlet excited state (S) potential energy surface (PES). Time-dependent density functional theory (TD-DFT), employing BP86/TZVPP, is widely used to construct such PESs. Regardless of the environment, the topology of the S PES of AdoCbl or MeCbl is marked by characteristic features, namely the metal-to-ligand charge transfer (MLCT) and ligand field (LF) regions. Conversely, the relative energetics of these electronic states are affected by the environment. Applications and outlooks for Cbl photochemistry are also discussed.
生物活性维生素 B 衍生物，甲钴胺（MeCbl）和腺苷钴胺（AdoCbl），是普遍存在的有机金属辅因子。除了在酶催化中的关键作用外，B 辅因子还具有复杂的光解性质，这一直是实验和理论研究的目标。随着最近发现 B 依赖性光受体，人们越来越需要阐明这些系统的潜在光化学机制。本章总结了 MeCbl 和 AdoCbl 依赖性酶的光解性质，特别强调了辅因子环境对激发态过程的影响。这些系统包括分离的 MeCbl 和 AdoCbl 以及酶，乙醇胺氨裂合酶（EAL），谷氨酸变位酶（GLM），蛋氨酸合酶（MetH）和光受体 CarH。确定每个系统的光解机制的核心是分析最低单线态激发态（S）势能面（PES）。时间依赖密度泛函理论（TD-DFT），采用 BP86/TZVPP，广泛用于构建这种 PES。无论环境如何，AdoCbl 或 MeCbl 的 S PES 的拓扑结构都以特征为标志，即金属-配体电荷转移（MLCT）和配体场（LF）区域。相反，这些电子态的相对能级受环境影响。还讨论了 Cbl 光化学的应用和前景。
