Myoglobin EXAFS

Chance et al. have also studied the EXAFS properties of the high-valent oxo-ferryl states of horseradish peroxidase, cytochrome c peroxidase, and myoglobin [144-146]. A two-atom-type constrained amplitude ratio fit and a three-atom-type consistency test were used for the analysis of the EXAFS data [144,146]. These analytical methods differ from that used by Hodgson and co-workers... 

EXAFS data for the proposed Fe =0 myoglobin derivative have also been reported by Chance et al. [146]. A short Fe=0 bond distance of 1.69 A was reported, together with evidence that the iron had been oxidized to Fe. The data clearly indicate that this myoglobin derivative has the expected Fe =0 structure. (See Note in Proof No. 2.)... 

Chance et al. have also investigated cytochrome c peroxidase Compound I (Compound ES) with EXAFS spectroscopy and found that it, too, has a short Fe-O bond of 1.67+0.04 A [145]. As discussed earlier, cytochrome c peroxidase Compound I is thought to contain an Fe =0 complex with a protein-centered radical [Fe =0]R [71]. Comparative crystallography of cytochrome c peroxidase Compound I and the native ferric enzyme [154] have been interpreted in terms of a short, strong Fe=0 double bond just as indicated by the results of EXAFS spectroscopy [145]. Thus, consensus has been reached that short Fe=0 bonds ( 1.65 A) are present for the Compound I derivative of horseradish peroxidase, the Compound I intermediate of cytochrome c peroxidase, and the related myoglobin complex (Table 2). 

The Fe-Na,i bonds of the Compound I states of horseradish peroxidase and cytochrome c peroxidase were reported to be 1.93 and 1.91 A, respectively, vs. 2.11 A for the oxo-iron(IV) derivative of myoglobin [144]. It must again be noted that there is disagreement [107] as to whether EXAFS data of... 

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