Ferric-hydroperoxo state

Spectroscopic and crystallographic studies indicate that the active site is six-coordinate in the Fe state, with four equatorial histidine ligands and axial cysteinate and monodentate glutamate ligands, and five-coordinate with a vacant coordination site as a result of loss of the glutamate ligand on reduction to the Fe state (Figure 2(c)).Optically monitored pulse radiolysis have revealed one or two transient catalytic intermediates that are proposed to correspond to a ferric-peroxo and ferric-hydroperoxo species and a transient ferric-peroxo species with a side-on peroxo has been spectroscopically characterized in samples frozen rapidly in the presence of The proposed mechanistic... 

SCHEME 4.3 Cytochrome P450 and peroxidase pathways to hydroperoxo-ferric intermediate or Compound 0 (5). Ferric cytochrome P450 (1) is reduced to the ferrous state (2), which can hind dioxygen to form oxy-ferrous complex (3). Reduction of this complex results in the formation of peroxo-ferric complex (4), which is protonated to give hydroperoxo-ferric complex (5). The same hydroperoxo-ferric complex is formed in peroxidases and catalases via reaction with hydrogen peroxide. 

X-ray crystal stmcture of hydroperoxo-ferric complex in CPO was determined as a result of cryogenic photoreduction of oxy-ferrous precursor during data collection in the synchrotron beam.133 Three data sets with low, medium, and high dose have been prepared from the data collected on multiple crystals with the goal to resolve the structures with well-defined redox state. Because of the fast reduction, the low-dose data set already had sufficient contribution of Compound 0, and the stmcture of Compound III could not be determined. The medium-dose data set was resolved to 1.75 A resolution and revealed a well-defined 0-0 ligand with 100% occupancy. Assignment of this stmcture to hydroperoxo- ferric versus peroxo-ferric was done based on the QM/MM calculation. 

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