Reaction mechanism of cobalt-substituted homoprotocatechuate 2,3-dioxygenase: a QM/MM study.
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.
Department of Chemistry, Renmin University of China, Beijing, 100872, China.
Lili
L
Cao
Department of Chemistry, Renmin University of China, Beijing, 100872, China.
Geng
G
Dong
Department of Chemistry, Renmin University of China, Beijing, 100872, China.
Wenzhen
W
Lai
D002396:Catechols / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D049308:Dioxygenases / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D011789:Quantum Theory; D017382:Reactive Oxygen Species / Q000737:chemistry
D002396:Catechols; D017382:Reactive Oxygen Species; D003035:Cobalt; D049308:Dioxygenases; C020055:3,4-dihydroxyphenylacetate 2,3-dioxygenase; D010100:Oxygen; C001833:4-nitrocatechol