Electron Nuclear Double Resonance (Endor) of Metalloenzymes

Hoffman, Brian M.; Gurbiel, Ryszard J.; Werst, M.; Sivaraja, M.

doi:10.1016/b978-0-444-88050-5.50020-3

Cited by 40 publications

(74 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As such, it lends itself well to the determination of the metrical parameters that relate the position of nuclei being examined to the g tensor, and ultimately to the molecular frame. 34,35 However, when g anisotropy is substantial, as in the present study, the general form of this interaction must be employed, eq 2,

{\overset{H}{true}}_{DD} = {normalg}_{normaln} {normalβ}_{normaln} \sum_{i} {\overset{μ}{true}}_{i} \cdot {normalT}_{i} \cdot \hat{normalI}

which employs the orientation dependent magnetic moment, μ̂ i = β e B o [ Ŝ · g · b ] in the presence of an external field, B o = B o b. 36 This leads to a non-symmetric dipolar coupling matrix that does not lend itself to a simple determination of its orientation within the molecular frame through coordinate transformations based on rotation matrices and Euler angles.…”

Section: Resultsmentioning

confidence: 99%

Modeling the Signatures of Hydrides in Metalloenzymes: ENDOR Analysis of a Di-iron Fe(μ-NH)(μ-H)Fe Core

et al. 2012

Self Cite

View full text Add to dashboard Cite

The application of 35 GHz pulsed EPR and ENDOR spectroscopies has established that the biomimetic model complex L3Fe(μ-NH)(μ-H)FeL3 (L3 = [PhB(CH2PPh2)3]-) complex, 3, is a novel S = ½ type-III mixed-valence di-iron II/III species, in which the unpaired electron is shared equally between the two iron centers. 1,2H and 14,15N ENDOR measurements of the bridging imide are consistent with an allyl radical molecular orbital model for the two bridging ligands. Both the (μ-H) and the proton of the (μ-NH) of the crystallographically characterized 3 show the proposed signature of a ‘bridging’ hydride that is essentially equidistant between two ‘anchor metal ions: a rhombic dipolar interaction tensor, T ≈ [T, -T, 0]. The point-dipole model for describing the anisotropic interaction of a bridging H as the sum of the point-dipole couplings to the ‘anchor’ metal ions reproduces this signature with high accuracy, as well as the axial tensor of a terminal hydride, T ≈ [-T, -T, 2T], thus validating both the model and the signatures. This validation in turn lends strong support to the assignment, based on such a point-dipole analysis, that the molybdenum-iron cofactor of nitrogenase contains two [Fe-H--Fe] bridging-hydride fragments in the catalytic intermediate that has accumulated four reducing equivalents (E4). Analysis further reveals a complementary similarity between the isotropic hyperfine couplings for the bridging hydrides in 3 and E4. This study provides a foundation for spectroscopic study of hydrides in a variety of reducing metalloenzymes in addition to nitrogenase.

show abstract

{\overset{H}{true}}_{DD} = {normalg}_{normaln} {normalβ}_{normaln} \sum_{i} {\overset{μ}{true}}_{i} \cdot {normalT}_{i} \cdot \hat{normalI}

Section: Resultsmentioning

confidence: 99%

Modeling the Signatures of Hydrides in Metalloenzymes: ENDOR Analysis of a Di-iron Fe(μ-NH)(μ-H)Fe Core

et al. 2012

Self Cite

View full text Add to dashboard Cite

show abstract

“…All CW Q-band EPR/ ENDOR spectra were recorded at 2 K in dispersion mode, under “rapid passage” conditions, which gives an absorption line shape. 36 UV–vis spectra of the samples in 4 mm o.d. quartz tubes were measured at 77 K through immersion in a liquid N2 finger dewar with a USB 2000 spectrophotometer (Ocean Optics, Inc.).…”

Section: Methodsmentioning

confidence: 99%

Role of the Proximal Cysteine Hydrogen Bonding Interaction in Cytochrome P450 2B4 Studied by Cryoreduction, Electron Paramagnetic Resonance, and Electron–Nuclear Double Resonance Spectroscopy

Davydov

Shanmugam

et al. 2016

Biochemistry

Self Cite

View full text Add to dashboard Cite

Crystallographic studies have shown that the F429H mutation of cytochrome P450 2B4 introduces an H-bond between His 429 and the proximal thiolate ligand, Cys 436, without altering the protein fold but sharply decreases the enzymatic activity and stabilizes the oxyferrous P450 2B4 complex. To characterize the influence of this hydrogen bond on the states of the catalytic cycle we have used radiolytic cryoreduction combined with EPR and ENDOR spectroscopy to study and compare their characteristics for wild type (WT) P450 2B4 and the F429H mutant. (i) The addition of an H-bond to the axial Cys436 thiolate significantly changes the EPR signals of both low-spin and high-spin heme-iron (III) and the hyperfine couplings of the heme-pyrrole 14N, but has relatively little effect on the 1H ENDOR spectra of the water ligand in the six-coordinate low-spin ferriheme state. These changes indicate that the H-bond introduced between His and the proximal cysteine decreases the S→Fe electron donation and weakens the Fe(III)-S bond. (ii) The added H-bond changes the primary product of cryoreduction of the Fe(II) enzyme, which is trapped in the conformation of the parent Fe(II) state. In wild-type enzyme the added electron localizes on the porphyrin, generating an S = 3/2 state with the anion radical exchange-coupled to the Fe (II). In the mutant it localizes on the iron, generating a S = ½ Fe(I) state. (iii) The additional H-bond has little effect on g-values and 1H, 14N hyperfine couplings of the cryogenerated, ferric hydroperoxo intermediate but noticeably slows its decay during cryoannealing. (iv) In both WT and mutant enzyme, this decay shows a significant solvent kinetic isotope effect, indicating that the decay reflects a proton-assisted conversion to Compound I (Cpd I). (v) We confirm that Cpd I formed during the annealing of the cryogenerated hydroperoxy intermediate and that it is the active hydroxylating species in both WT P450 2B4 and the F429H mutant.(vi) Our data also indicate that the added H-bond of the mutation diminishes the reactivity of Cpd I.

show abstract

“…Methods to compute ENDOR signals from transition metal complexes obtained at arbitrary field positions have been developed by Hoffman [173][174][175][176], Henderson [178][179], Gochev [180] and their coworkers. In general it is impossible to resolve the g-value extrema of all three principal values in EPR spectra, in order to obtain single crystal-like ENDOR spectra from all three principal directions.…”

Section: Simulation Of Endor Powder Spectramentioning

confidence: 99%

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Erickson

Lund

2014

Applications of EPR in Radiation Research

View full text Add to dashboard Cite

Applications of EPR and ENDOR simulations of relevance in radiation research involving free radicals, radical pairs, triplet states and to less extent metal complexes are treated. Early fundamental work involving in situ radiolysis of liquids and stickplot analysis of spectra is reviewed, while single crystal analysis is only briefly discussed. The analysis of data obtained with continuous wave methods of species trapped in disordered solids, "powders" is emphasized. Simulations based on first and second order and exact theory are described and exemplified. Methods to obtain parameters for the dynamics of radicals in irradiated solids and for the simulation of spectra at microwave saturation are discussed. Procedures for the simulation of powder ENDOR spectra of radicals are described in detail, with special emphasis on the influence of nuclear quadrupole couplings due to nuclei with I ≥ 1. EPR and ENDOR simulation programs known to us are presented in an Appendix, including addresses for downloading when available.

show abstract

Electron Nuclear Double Resonance (Endor) of Metalloenzymes

Cited by 40 publications

References 60 publications

Modeling the Signatures of Hydrides in Metalloenzymes: ENDOR Analysis of a Di-iron Fe(μ-NH)(μ-H)Fe Core

Modeling the Signatures of Hydrides in Metalloenzymes: ENDOR Analysis of a Di-iron Fe(μ-NH)(μ-H)Fe Core

Role of the Proximal Cysteine Hydrogen Bonding Interaction in Cytochrome P450 2B4 Studied by Cryoreduction, Electron Paramagnetic Resonance, and Electron–Nuclear Double Resonance Spectroscopy

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Contact Info

Product

Resources

About