ChemInform Abstract: Structural Characterization of Horseradish Peroxidase Using EXAFS Spectroscopy. Evidence for Fe=O Ligation in Compounds I and II

Penner‐Hahn, James E.; Eble, K S; McMurry, Thomas J.; Renner, Mark W.; Balch, Alan L.; Groves, John T.; Dawson, John H.

doi:10.1002/chin.198715052

Cited by 11 publications

(18 citation statements)

References 1 publication

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“…Calculations have provided ferryl bond distances on the order of 1.65 Å for these intermediates [10][11][12][13][14][15]. This value has been in good agreement with bond distances obtained from experiments on enzymatic systems as well synthetic ferryl porphyrins [16][17][18]. Until recently, there had been little evidence to suggest that these seemingly well-characterized intermediates were anything other than authentic Fe IV oxos.…”

Section: Introductionsupporting

confidence: 56%

“…EXAFS investigations of enzymatic ferryls have generally yielded Fe-O bond lengths that are similar to those found in synthetic Fe IV O porphyrins (%1.65 Å ) [16][17][18], two exceptions being measurements on CPO-II and HRP-II [7,27]. The results of EXAFS experiments on HRP-II have proved particularly problematic: Two independent studies found oxo-like distances, while a third obtained an Fe-O bond of 1.93 Å .…”

Section: Ferryl Protonationmentioning

confidence: 86%

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On the status of ferryl protonation

Behan

Green

2006

Journal of Inorganic Biochemistry

118

174

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Section: Introductionsupporting

confidence: 56%

Section: Ferryl Protonationmentioning

confidence: 86%

On the status of ferryl protonation

Behan

Green

2006

Journal of Inorganic Biochemistry

118

174

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“…This intermediate was identified as an 1 A few exceptional cases with much longer bond lengths were also reported, but are attributed to either experimental pitfalls or unconventional data analysis oxoiron(IV) porphyrin cation radical complex, [(TMP c 7)Fe IV (O)] c (1), based on UV-vis [16], NMR [16], Mössbauer [16], EPR [17], resonance Raman (RR) [18,19], and EXAFS [20] spectroscopies. Similar to compounds I of the various enzymes, complex 1 is a cationic complex with an additional axial ligand trans to the oxo ligand.…”

Section: Introductionmentioning

confidence: 90%

Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

et al. 1997

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A series of oxoiron(IV) porphyrin cation radical complexes was investigated as compound I analogs of cytochrome P-450. Both the spectroscopic features and the reactivities of the complexes in oxygen atom transfer to olefins were examined as a function of only one variable, the axial ligand trans to the oxoiron-(IV) bond. The results disclosed two important kinetic steps -electron transfer from olefin to oxoiron(IV) and intramolecular electron transfer from metal to porphyrin radical -which are affected differently by the axial ligands. The large kinetic barrier of the latter step in the reaction of olefins with the perchlorato-bound oxoiron(IV) porphyrin cation radical complex enabled the trapping of a reaction intermediate in which the metal, but not the porphyrin radical, is reduced. The first electron transfer step is probably followed by s-bond formation, which readily accounts for formation of isomerized organic products at low temperatures. It is finally postulated that part of the enhanced oxygenation activities of cytochrome P-450 monooxygenases and chloroperoxidases is due to a lowering of the energy barrier for the second electron transfer step via participation of their redox-active cysteinate ligand.

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“…For the HRP model the imidazole axial ligand has been truncated at the C g carbon and the C b attachment replaced with a hydrogen. A ferryl oxygen was then attached at 1.67 Å from the heme iron in all models, in accordance with known EXAFS Fe=O data for oxyferryl species [29] and a cryogenic X-ray structure of P450cam [25]. The initial porphyin models for both CPO-I and HRP-I models were obtained from these by replacing the protoporphyrin IX substituents with H atoms.…”

Section: Models Used and Choice Of Initial Geometriesmentioning

confidence: 99%

Proximal ligand effects on electronic structure and spectra of compound I of peroxidases

Harris

Loew

2001

J. Porphyrins Phthalocyanines

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ABSTRACT:Computational studies exploring the extent to which differences in proximal axial ligands modulate structure, spectra, and function of peroxidases have been performed. To this end, three heme models of compound I were characterized differing only in the axial ligand. The axial ligands considered were L=ImH, Im À , that are alternative protonation models for a typical peroxidase with an imidazole ligand such as horseradish peroxidase (HRP-I), and L=SCH-that is a model for an unsual peroxidase, chloroperoxidase (CPO-I). Density functional calculations (DFTs) were performed to determine the optimized geometries and electronic structure of each of these three species. Their electronic spectra were also calculated at the DFT optimized geometries, using the INDO/S/CI method. The results of these studies led to the following conclusions: (1) the presence of the nearby Asp in a typical peroxidase does indeed decrease the energy required to deprotonate the imidazole making the two forms essentially degenerate, (2) neither the state of protonation of the imidazole ligand nor the change in axial ligand from an imidazole in typical peroxidases such as HRP to a mercaptide in CPO significantly alters the characteristics of the lowest energy spin state or the electronic structure of compound I in a way that can obviously affect function, (3) both the Im À and ImH forms of the peroxidase compound I (HRP-I) lead to the same dramatic reduction in intensity relative to the ferric resting form observed experimentally. However, only in the ImH form of HRP-I does the calculated relative shift of one component of the Soret bands relative to CPO-I agree with that observed in the transient spectra of HRP-I compared to CPO-I. These results taken together strongly indicate that factors other than the nature of the proximal axial ligand are the main determinants of function.

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ChemInform Abstract: Structural Characterization of Horseradish Peroxidase Using EXAFS Spectroscopy. Evidence for Fe=O Ligation in Compounds I and II

Abstract: 052ChemInform Abstract (for comparison, some porphyrin model compounds are also investigated).

Cited by 11 publications

References 1 publication

On the status of ferryl protonation

On the status of ferryl protonation

Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

Proximal ligand effects on electronic structure and spectra of compound I of peroxidases

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