Reduction of Oxy-Ferrous

Reduction of Oxy-Ferrous P450 and Formation of Peroxo-Ferric Complexes Properties, Stability, and Spectroscopy... 

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. 

Bec, N., Gorren, A. C., Voelker, C., Mayer, B., Lange, R., Reaction of neuronal nitric-oxide synthase with oxygen at low temperature. Evidence for reductive activation of the oxy-ferrous complex by tetrahydrobiopterin, J. Biol. Chem. 273 (1998), p. 13502-13508... 

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. 

Reduction of compound I by one electron produces compound II, which has the characteristics of a normal ferry 1-porphyrin complex, analogous to 2, i.e., (L)Fe (P)(0). Reaction of compound II with hydrogen peroxide produces compound III, which can also be prepared by reaction of the ferrous enzyme with dioxygen. It is an oxy form, analogous to oxymyoglobin, and does not appear to have a physiological function. The reactions producing these three forms and their proposed formulations are summarized in Reactions (5.85) to (5.88). 

R. Lange (1998). Reaction of neuronal nitric-oxide synthase with oxygen at low temperature. Evidence for reductive activation of the oxy-ferrous... 

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