Molecular-Level Insight into the Differential Oxidase and Oxygenase Reactivities of de NovoDue Ferri Proteins
摘要:
Using the single-chain due ferri (DFsc) peptide scaffold, the differential oxidase and oxygenase reactivities of two 4A -> 4G variants, one with two histidines at the diiron center (G4DFsc) and the other with three histidines (3His-G4DFsc(Mut3)), are explored. By controlling the reaction conditions, the active form responsible for 4-aminophenol (4-AP) oxidase activity in both G4DFsc and 3His-G4DFsc(Mut3) is determined to be the substrate-bound biferrous site. Using circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field (VTVH) MCD spectroscopies, 4-AP is found to bind directly to the biferrous sites of the DF proteins. In G4DFsc, 4-AP increases the coordination of the biferrous site, while in 3His-G4DFsc(Mut3), the coordination number remains the same and the substrate likely replaces the additional bound histidine. This substrate binding enables a two-electron process where 4-AP is oxidized to benzoquinone imine and O-2 is reduced to H2O2. In contrast, only the biferrous 3His variant is found to be active in the oxygenation of p-anisidine to 4-nitroso-methoxybenzene. From CD, MCD, and VTVH MCD, p-anisidine addition is found to minimally perturb the biferrous centers of both G4DFsc and 3His-G4DFsc(Mut3), indicating that this substrate binds near the biferrous site. In 3His-G4DFsc(Mut3), the coordinative saturation of one iron leads to the two-electron reduction of O-2 at the second iron to generate an end-on hydroperoxo-Fe(III) active oxygenating species.
Benzoquinone imines. Part 18. Kinetics and mechanism of oxidative coupling reactions involving N,N-bis-(2-hydroxyethyl)-p-phenylenediamine
作者:David J. Palling、Keith C. Brown、John F. Corbett
DOI:10.1039/p29860000065
日期:——
A kinetic and mechanistic study of oxidative coupling reactions of N,N-bis-(2-hydroxyethyl)-p-phenylenediamine with m-phenylenediamines, phenols, and acetoacetanilide is described. The reactions involve the rapid establishment of an equilibrium between N,N-bis-(2-hydroxyethyl)-p-benzoquinone di-imine and a hydroxy-amine intermediate (3). Competition between direct coupling of N,N-bis-(2-hydroxyethyl)-p-benzoquinone
Not just a four-helix bundle: The use of a diiron-binding four-helix bundle scaffold with an asymmetric active site leads to an enhancement in selectivity of the iron-catalyzedoxidative coupling of phenols. The stabilization of the oxidized intermediate in the binding pocket enables the net four-electron O2 reduction, without release of any detectable H2O2.
不仅是四螺旋束:具有不对称活性位点的二铁结合四螺旋束支架的使用会导致铁催化的酚氧化偶联的选择性增强。结合口袋中被氧化的中间体的稳定化使得四电子O 2净减少,而不会释放任何可检测的H 2 O 2。