Electron spin echo envelope modulation studies of the semiquinone anion radical of cholesterol oxidase from <i>Brevibacterium sterolicum</i>

Medina, Milagros; Vrielink, Alice; Cammack, Richard

doi:10.1016/s0014-5793(96)01372-5

Cited by 14 publications

(18 citation statements)

References 23 publications

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“…In previous works, interaction parameters for N(1) and N(3) for cholesterol oxidase, flavodoxin, and FNR semiquinones were already described from 3P ESEEM experiments. Now, our HY-SCORE measurements confirm the tentative assignment from 1D-ESEEM features to these nitrogens (Medina & Cammack, 1996;Medina et al, 1997).…”

Section: (B) Correlation Peaks At (3 Mhz 5 Mhz)supporting

confidence: 79%

“…Since peaks corresponding to N(A) in cholesterol oxidase semiquinone are quite narrow, it is likely that the anisotropic hyperfine term for N(A) in this sample is very small compared to the isotropic one. Just minor changes have been found for all the parameters calculated for cholesterol oxidase semiquinone HYSCORE spectra with regard to those already reported in 1D-ESEEM (Medina et al, 1997). Nevertheless, the improvement of the signal:noise ratio achieved by the 2D techniques, together with the higher resolution of the HYSCORE experiment as compared with 3P ones, give a better accuracy for the calculated parameter values.…”

Section: (B) Correlation Peaks At (3 Mhz 5 Mhz)mentioning

confidence: 45%

“…To our knowledge this is the first report on a flavoprotein semiquinone HYSCORE study. We show that 1D-ESEEM signals assigned to weakly interacting nitrogen in cholesterol oxidase, flavodoxin, and FNR semiquinones (Medina et al, 1997;Medina & Cammack, 1996) possibilities in the study of the environment of the flavin cofactor in proteins and in the modulation of its properties by the apoprotein.…”

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confidence: 93%

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One- and Two-Dimensional ESEEM Spectroscopy of Flavoproteins

et al. 1997

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One- and two-dimensional (1D and 2D) electron spin echo envelope modulation (ESEEM) spectroscopy was applied to study the flavin cofactors in the neutral semiquinone states of flavodoxin and ferredoxin-NADP+ reductase (FNR) from the cyanobacterium Anabaena PCC 7119, and the anionic semiquinone state of cholesterol oxidase from Brevibacterium sterolicum. High-resolution crystal structures are available for all these proteins. Three- and 4-pulse ESEEM and hyperfine sublevel correlation spectroscopy (HYSCORE) techniques at X-band were used. HYSCORE spectra showed correlations between transitions caused by interaction of the isoalloxazine unpaired electronic spin present in the semiquinone state with several nitrogen and hydrogen nuclei. Measurements of isotopic labeled samples ([15N]FMN flavodoxin and [2H]flavodoxin) allowed the assignment of all the detected transitions to nuclei belonging to the FMN cofactor group. Interactions of nitrogens in positions 1 and 3 of the isoalloxazine ring were determined to have isotropic hyperfine coupling constants in the 1-2 and 0.5-1 MHz ranges for all the different flavoprotein semiquinones studied. Information about the quadrupolar term of these nuclei was also obtained. An intense correlation in the negative quadrant was detected. It has been associated to the strongly interacting N(10) nucleus. The complete hyperfine term parameters (including the sign) were obtained from detailed analysis of this signal, being the quadrupolar parameter, K, also estimated. Another correlation in the HYSCORE spectra, corresponding to hydrogen bound to the N(5) position in neutral flavin semiquinones, was detected. Its interaction parameters were also determined. This study demonstrates that ESEEM spectroscopy, and in particular the HYSCORE technique, are of particular utility for detecting and assigning nuclear transition frequencies in flavoprotein semiquinones. Moreover, the results reported here are complementary to ENDOR studies, and both techniques together provide an important tool for obtaining information about spin distribution in the flavin ring of flavoproteins in the semiquinone state.

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Section: (B) Correlation Peaks At (3 Mhz 5 Mhz)supporting

confidence: 79%

Section: (B) Correlation Peaks At (3 Mhz 5 Mhz)mentioning

confidence: 45%

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confidence: 93%

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One- and Two-Dimensional ESEEM Spectroscopy of Flavoproteins

et al. 1997

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“…With the commercial availability of pulsed EPR instrumentation, other pulsed methods such as electron‐spin echo envelope modulation or hyperfine sublevel correlation spectroscopy, which are quite useful for studying specific hyperfine and quadrupolar couplings, have been applied to flavoproteins [51,54,55]. These studies have been reviewed recently [40].…”

Section: Epr and Endor Investigations Of Flavoproteinsmentioning

confidence: 99%

New roles of flavoproteins in molecular cell biology: Blue‐light active flavoproteins studied by electron paramagnetic resonance

2009

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Exploring enzymatic mechanisms at a molecular level is one of the major challenges in modern biophysics. Based on enzyme structure data, as obtained by X‐ray crystallography or NMR spectroscopy, one can suggest how substrates and products bind for catalysis. However, from the 3D structure alone it is very rarely possible to identify how intermediates are formed and how they are interconverted. Molecular spectroscopy can provide such information and thus supplement our knowledge on the specific enzymatic reaction under consideration. In the case of enzymatic processes in which paramagnetic molecules play a role, EPR and related methods such as electron‐nuclear double resonance (ENDOR) are powerful techniques to unravel important details, e.g. the electronic structure or the protonation state of the intermediate(s) carrying (the) unpaired electron spin(s). Here, we review recent EPR/ENDOR studies of blue‐light active flavoproteins with emphasis on photolyases that catalyze the enzymatic repair of UV damaged DNA, and on cryptochrome blue‐light photoreceptors that act in several species as central components of the circadian clock.

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“…due to substrate binding, altered geometries of hydrogen bonds, surrounding amino acids have been shown experimentally535455565758596061 and theoretically436263. If such inherent heterogeneities existed, they could potentially lead to significantly larger levels of variation than the 2% level assumed here.…”

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confidence: 69%

Inhomogeneous ensembles of radical pairs in chemical compasses

Procopio

Ritz

2016

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The biophysical basis for the ability of animals to detect the geomagnetic field and to use it for finding directions remains a mystery of sensory biology. One much debated hypothesis suggests that an ensemble of specialized light-induced radical pair reactions can provide the primary signal for a magnetic compass sensor. The question arises what features of such a radical pair ensemble could be optimized by evolution so as to improve the detection of the direction of weak magnetic fields. Here, we focus on the overlooked aspect of the noise arising from inhomogeneity of copies of biomolecules in a realistic biological environment. Such inhomogeneity leads to variations of the radical pair parameters, thereby deteriorating the signal arising from an ensemble and providing a source of noise. We investigate the effect of variations in hyperfine interactions between different copies of simple radical pairs on the directional response of a compass system. We find that the choice of radical pair parameters greatly influences how strongly the directional response of an ensemble is affected by inhomogeneity.

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Electron spin echo envelope modulation studies of the semiquinone anion radical of cholesterol oxidase from Brevibacterium sterolicum

Cited by 14 publications

References 23 publications

One- and Two-Dimensional ESEEM Spectroscopy of Flavoproteins

One- and Two-Dimensional ESEEM Spectroscopy of Flavoproteins

New roles of flavoproteins in molecular cell biology: Blue‐light active flavoproteins studied by electron paramagnetic resonance

Inhomogeneous ensembles of radical pairs in chemical compasses

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