2 publications

2 publications

Manganese(V) Porphycene Complex Responsible for Inert C–H Bond Hydroxylation in a Myoglobin Matrix

Oohora, K.

J. Am. Chem. Soc. 2017, 139, 18460-18463, 10.1021/jacs.7b11288

A mechanistic study of H2O2-dependent C–H bond hydroxylation by myoglobin reconstituted with a manganese porphycene was carried out. The X-ray crystal structure of the reconstituted protein obtained at 1.5 Å resolution reveals tight incorporation of the complex into the myoglobin matrix at pH 8.5, the optimized pH value for the highest turnover number of hydroxylation of ethylbenzene. The protein generates a spectroscopically detectable two-electron oxidative intermediate in a reaction with peracid, which has a half-life up to 38 s at 10 °C. Electron paramagnetic resonance spectra of the intermediate with perpendicular and parallel modes are silent, indicating formation of a low-spin MnV-oxo species. In addition, the MnV-oxo species is capable of promoting the hydroxylation of sodium 4-ethylbenzenesulfonate under single turnover conditions with an apparent second-order rate constant of 2.0 M–1 s–1 at 25 °C. Furthermore, the higher bond dissociation enthalpy of the substrate decreases the rate constant, in support of the proposal that the H-abstraction is one of the rate-limiting steps. The present engineered myoglobin serves as an artificial metalloenzyme for inert C–H bond activation via a high-valent metal species similar to the species employed by native monooxygenases such as cytochrome P450.


Metal: Mn
Ligand type: Amino acid; Porphycene
Host protein: Myoglobin (Mb)
Anchoring strategy: Reconstitution
Optimization: ---
Reaction: Hydroxylation
Max TON: 13
ee: ---
PDB: 5YL3
Notes: ---

Photoinduced Electron Transfer within Supramolecular Hemoprotein Co-Assemblies and Heterodimers Containing Fe and Zn Porphyrins

Oohora, K.

J. Inorg. Biochem. 2019, 193, 42-51, 10.1016/j.jinorgbio.2019.01.001

Electron transfer (ET) events occurring within metalloprotein complexes are among the most important classes of reactions in biological systems. This report describes a photoinduced electron transfer between Zn porphyrin and Fe porphyrin within a supramolecular cytochrome b562 (Cyt b562) co-assembly or heterodimer with a well-defined rigid structure formed by a metalloporphyrin–heme pocket interaction and a hydrogen-bond network at the protein interface. The photoinduced charge separation (CS: kCS = 320–600 s−1) and subsequent charge recombination (CR: kCR = 580–930 s−1) were observed in both the Cyt b562 co-assembly and the heterodimer. In contrast, interestingly, no ET events were observed in a system comprised of a flexible and structurally-undefined co-assembly and heterodimers which lack the key hydrogen-bond interaction at the protein interface. Moreover, analysis of the kinetic constants of CS and CR of the heterodimer using the Marcus equation suggests that a single-step ET reaction occurs in the system. These findings provide strong support that the rigid hemoprotein-assembling system containing an appropriate hydrogen-bond network at the protein interface is essential for monitoring the ET reaction.


Metal: Fe; Zn
Ligand type: Protoporphyrin IX
Host protein: Cytochrome b562
Anchoring strategy: Cystein-maleimide; Supramolecular
Optimization: Chemical & genetic
Reaction: Electron transfer
Max TON: ---
ee: ---
PDB: ---
Notes: ---