Department of Chemistry, Renmin University of China, Beijing, 100872, China.
J Phys Chem B. 2015 Apr 2;119(13):4608-16. doi: 10.1021/acs.jpcb.5b00613. Epub 2015 Mar 18.
The reaction mechanisms of cobalt-substituted homoprotocatechuate 2,3-dioxygenase (Co-HPCD) with electron-rich substrate homoprotocatechuate (HPCA) and electron-poor substrate 4-nitrocatechol (4NC) were investigated by quantum mechanical/molecular mechanical (QM/MM) calculations. Our results demonstrated that the Co-O2 adducts has doublet ground state with a Co(III)-O2(•-) character when 4NC was used as the substrate, in good agreement with the EPR spectroscopic experiment. The reactive oxygen species is the doublet Co(III)-O2(•-) for Co-HPCD/4NC and the quartet SQ(•↑)-Co(II)-O2(•-↓) species for Co-HPCD/HPCA, indicating that the substrate plays important roles in the dioxygen activation by Co-HPCD. B3LYP was found to overestimate the rate-limiting barriers in Co-HPCD. TPSSh predicts barriers of 21.5 versus 12.0 kcal/mol for Co-HPCD/4NC versus Co-HPCD/HPCA, which is consistent with the fact that the rate of the reaction is decreased when the substrate was changed from HPCA to 4NC.
采用量子力学/分子力学(QM/MM)计算方法研究了富电子底物邻苯二酚（HPCA）和缺电子底物 4-硝基邻苯二酚（4NC）与钴取代的原儿茶酸 2,3-双加氧酶（Co-HPCD）的反应机理。结果表明，当 4NC 作为底物时，Co-O2 加合物具有二重态基态，具有 Co(III)-O2(•-)特征，与 EPR 光谱实验结果一致。对于 Co-HPCD/4NC，反应性氧物种为 Co(III)-O2(•-)，而对于 Co-HPCD/HPCA，反应性氧物种为 quartet SQ(•↑)-Co(II)-O2(•-↓)物种，表明底物在 Co-HPCD 对氧的活化中起重要作用。B3LYP 被发现高估了 Co-HPCD 中的限速障碍。TPSSh 预测 Co-HPCD/4NC 与 Co-HPCD/HPCA 的障碍分别为 21.5 和 12.0 kcal/mol，这与反应速率降低的事实一致，当底物从 HPCA 变为 4NC 时。
