Simulation Methods for Looping Transitions

Gaffney, Betty J.; Silverstone, Harris J.

doi:10.1006/jmre.1998.1526

Cited by 19 publications

(32 citation statements)

References 13 publications

(38 reference statements)

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“…There are two or more resonant fields for a single angular orientation because the separation of the energy levels is a curved function of magnetic field [12]. There is a high density of large intensity factors at the magnetic field of about 160 mT, with highest intensities occurring in the molecular yz plane at B of about 52°.…”

Section: Resultsmentioning

confidence: 98%

“…6. Dependence of the intensity factor [12] on magnetic field for the 3 -5 transition of Se = 5/2 (upper) is compared with the derivative EPR spectrum calculated for this transition (lower) for a calculation with D and E = 0.08 and 0.015 cm -', respectively, and microwave frequency of 9.26 GHz. The intensity factor was calculated with Eq.…”

Section: Resultsmentioning

confidence: 99%

“…The line shapes for transitions between energy levels that have extended regions of separation equal to the microwave energy took into account the special considerations for "looping" transitions [12]. Other EPR spectra including ones with manganous nuclear hyperfine splitting were simulated with the XSophe program marketed by Bruker and developed by G. R. Hanson and co-workers [13].…”

Section: Methodsmentioning

confidence: 99%

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Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure

Gaffney

Oliw

2001

Appl. Magn. Reson.

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A new variant of lipoxygenases, one containing manganese instead of iron, is characterized by electron paramagnetic resonance (EPR) at two frequencies. In the manganous state (S(e) = 5/2), maganese lipoxygenase (MnLO) yields very broad X-band (9.2 GHz) EPR signals, extending over about 800 mT. In contrast, at W-band (94 GHz), the signal is much simplified, consisting of nested transitions centered near the free electron g-value. Computer simulation has been employed to derive estimates of the zero-field splittings for MnLO, with data from these two EPR frequencies. The general features of both X- and W-band spectra are fit, first, by simulations with S(e) = 5/2, but no nuclear hyperfine splitting. The simulations are then refined by inclusion of the hyperfine splitting. On the basis of the simulations, the ranges of zero-field splitting parameters are D = +0.07 to +0.10 cm(-1), and E/D = 0.13 to 0.23. Comparison of the value of D for MnLO with that of other manganese-containing proteins suggests that MnLO has three N-ligands to the metal center and O-ligands in the remainder of 6 coordination positions. The coordination environment of MnLO is similar to that in iron lipoxygenases.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure

Gaffney

Oliw

2001

Appl. Magn. Reson.

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“…A distribution of E/D indicates conformational strain and has been observed for other high-spin ferric proteins. 12,13 A representative set of spectra calculated for different values of E/D is depicted in the right hand inset of Fig. 2.…”

Section: B Conventional Epr Spectramentioning

confidence: 99%

Magnetic and optical anisotropy of Clostridium pasteurianum rubredoxin from optically detected electron paramagnetic resonance

Börger

Suter

2001

The Journal of Chemical Physics

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The high-spin Fe͑III͒-center of oxidized rubredoxin from Clostridium pasteurianum shows a complicated, temperature-dependent EPR spectrum. We combine conventional EPR spectroscopy with optically detected EPR ͑ODEPR͒ to elucidate the electronic structure of this protein metal center. The ODEPR experiment, which can be considered as coherent Raman scattering or modulated magnetic circular dichroism ͑MCD͒, yields spectra that depend on the relative orientation of optical and magnetic dipole moments. A detailed analysis of the spectra shows that they correspond to a zero-field splitting of Dϭϩ46.3 GHz and a strong rhombic distortion with E/D ϭ0.25. In the frozen solution, conformational strain gives rise to variation of the rhombicity, which can be measured quantitatively from the EPR line shape. Analysis of the ODEPR line shapes yields the orientation of the optical anisotropy with respect to the magnetic g-tensor. We compare the results from this study to published results on EPR, optical spectroscopy, and MCD.

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“…Looping transitions occur when energy levels have avoided crossings, a case that is found when the microwave frequency is on the order of zero-field splittings. In these transitions, the separation of levels near a resonance does not diverge with field, and the line width is so broad that the transition at selected angles in an oriented sample may actually disappear [6]. At the other extreme, when the operating frequency is much greater than the zero-field splitting in an S> 1/2 system, observed line widths may decrease relative to those at lower frequency because distributions of zero-field parameters contribute to a decreased extent.…”

Section: Introductionmentioning

confidence: 98%

Disorder at metal sites in proteins: A high-frequency-EMR study

et al. 1999

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High-frequency EMR of metalloprotein samples offers considerable potential for providing improvements in characterization of metal centers. For those metal ions that are studied at low temperature, line widths may be frequency-dependent, depending on the terms that limit the widths. Here we examine apparent EMR line widths and line shapes in some representative metalloprotein samples at two frequencies: -9.2 GHz (X-band) and -94 GHz (W-band). Samples of the same size were measured at both frequencies. The samples include cupric ion in lactoferrin, high-spin ferric ion in diferric transferrin and high-spin ferric heme in catalase. For the approximately tenfold increase in EMR frequency, the observed line widths increased tenfold or less for the samples chosen. Distributions in one or more spin Hamiltonian parameters can account for these line width dependences on EMR frequency in the lactoferrin and transferrin samples, while molecular heterogeneity is a likely contributor to the catalase frequency-dependent line width. These measurements over frequencies differing by a factor of ten also contributed new insight for simulation of the EMR spectra of diferric transferrin.

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Simulation Methods for Looping Transitions

Cited by 19 publications

References 13 publications

Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure

Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure

Magnetic and optical anisotropy of Clostridium pasteurianum rubredoxin from optically detected electron paramagnetic resonance

Disorder at metal sites in proteins: A high-frequency-EMR study

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