Peroxodiferric intermediate

Theil, E.C. and Huynh, B.H. (1998) Direct spectroscopic and kinetic evidence for the involvement of a peroxodiferric intermediate during the ferroxidase reaction in fast ferritin mineralization. Biochemistry, 37, 9871-9876. 

The stoichiometry of 2Fe(II)/02, and the structure of the ferroxidase iron site suggest that the first step after iron (II) binding would be transfer of two electrons, one from each Fe(II), to a dioxygen molecule bound at the same site, to give a formal peroxodiferric intermediate formally this represents dioxygen binding, followed by Fe(II) oxidation (Equations (19.2) and (19.3)) ... 

The detection of a peroxodiferric intermediate in the ferritin ferroxidase reaction establishes the ferritin ferroxidase site as being very similar to the sites in the 02-activating (/x-carboxylato)diiron enzymes. However, in ferritins, the peroxodiferric intermediate forms diferric oxo or hydroxo precursors, which are transferred to biomineralization sites with release of hydrogen peroxide. 

Broadwater, J. A., Ai, J., Loehr, T. M., Sanders-Loehr, J., and Fox, B. G., 1998, Peroxodiferric intermediate of stearoyl-acyl carrier protein A9 desaturase oxidase reactivity during single turnover and implications for the mechanism of desaturation. Biochemistry 37 14664nl4471. 

During the ferroxidation reaction, a blue color with an absorption maximum of 650 run appears. This persists in oxygen-limited conditions and decays as iron oxidation proceeds. " In frog H-chain ferritin, resonance Raman studies indicate a similar absorption is associated with an Fe(III)-tyrosinate. Harrison and Treffty have considered these and other studies and attribute the transient color to formation of a /x-l,2-peroxodiferric intermediate, which decays to a more stable /x-oxodiferric species as occurs in methane monooxygenase, ribonucleotide reductase, and model compounds. Protein radicals distinct from reactive oxygen species have been observed that have been attributed to damage caused by Fenton chemistry. ... 

Figure 16-2 Possible peroxide binding modes for the peroxodiferric intermediates found in MMOH, D84E-R2, and recombinant frog M ferritin.

Table 16-1 Spectroscopic properties of peroxodiferric intermediates in certain proteins and peroxodiferric compounds... 

The ferrooxidase site is a dinuclear iron center (see Section 8) in which two iron ions (probably Fe2+) are bound as in Fig. 16-4. They are then converted to Fe3+ ions by 02, which may bind initially to the Fe2+, forming a transient blue intermediate that is thought to have a peroxodiferric structure, perhaps of the following type.71 73 Reaction of this intermediate with H20... 

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