EPR spectroscopy at very high field

Barra, Anne‐Laure; Brunel, Louis‐Claude; Robert, J. B.

doi:10.1016/0009-2614(90)87019-n

Cited by 141 publications

(83 citation statements)

References 6 publications

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“…285 GHz EPR spectra were recorded at 5 K in the Grenoble High Magnetic Field Laboratory (CNRS-MPI, Grenoble, France) as previously described (23). The frequency source used to generate a 285 GHz excitation is a Gunn-diode delivering a 95 GHz basic frequency, which is then tripled to obtain 285 GHz (system supplied by Radiometer Physics GmbH).…”

Section: Preparation Of the Anaerobic Fementioning

confidence: 99%

Restoring Proper Radical Generation by Azide Binding to the Iron Site of the E238A Mutant R2 Protein of Ribonucleotide Reductase fromEscherichia coli

Assarsson

Andersson

Högbom

et al. 2001

Journal of Biological Chemistry

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Section: Preparation Of the Anaerobic Fementioning

confidence: 99%

Restoring Proper Radical Generation by Azide Binding to the Iron Site of the E238A Mutant R2 Protein of Ribonucleotide Reductase fromEscherichia coli

Assarsson

Andersson

Högbom

et al. 2001

Journal of Biological Chemistry

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“…EPR spectroscopy at X-band, 9.62 GHz, and 245 GHz (using the 1223.67-m laser line of methanol gas as the frequency source for the EPR instrument) was done as before (16,20) using at maximum 3-G modulation amplitude. The 115-GHz spectrum was obtained with the same basic instrument set up (20) as at 245 GHz but using a Lithuanian (Elmika company) carcinotron as a source of frequencies for microwaves for the EPR. Simulations of the X-band EPR spectra were made as before (16) using iteration minimization routines to fit the spectra (28).…”

Section: Methodsmentioning

confidence: 99%

High Field EPR Studies of Mouse Ribonucleotide Reductase Indicate Hydrogen Bonding of the Tyrosyl Radical

Schmidt

Andersson

Barra

et al. 1996

Journal of Biological Chemistry

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Ribonucleotide reductase catalyzes by free radical chemistry the reduction of ribonucleotides to deoxyribonucleotides. The R2 protein of a class 1 ribonucleotide reductase contains a stable tyrosyl radical of neutral phenoxy character, which is necessary for normal enzymatic activity. Here we present the EPR spectra from the tyrosyl free radical in the R2 protein from mouse at 9.62, 115, and 245 GHz. We show that the g-value anisotropy of the mouse R2 radical, when precisely determined from high field EPR spectra, is similar to that of the hydrogen bonded dark stable Y D ⅐ tyrosyl radical of photosystem II and different from that of the Escherichia coli R2 radical. Because the g-value anisotropy is an important indicator of the hydrogen bonding status of the tyrosyl radical, this result suggests that the mouse R2 radical has its tyrosylate oxygen hydrogen bonded with a D 2 O exchangeable proton, whereas this hydrogen bond is absent in the E. coli enzyme. It is suggested that the observed proton may be derived from the tyrosine that will become a tyrosyl radical.Free radicals on tyrosyl residues have been found in the enzyme ribonucleotide reductase (RNR) 1 from several different sources, as well as in photosystem II (PSII) and prostaglandin H synthase (1). The highly regulated RNR catalyzes the reduction of ribonucleotides to deoxyribonucleotides, which are precursors in the synthesis of DNA in all living organisms (2-5).Several classes of RNR have been described. Class I enzymes contain a stable tyrosyl radical of neutral phenoxy type and a diferric iron-oxygen center in the small subunit protein R2 (2-5). The catalytically active form of class I RNR consists of a 1:1 complex of the two subunits, proteins R1 and R2, each of which is a homodimer. The crystal structures of Escherichia coli proteins R1 and R2 have been determined (6 -8). The tyrosyl radical, which is necessary for normal enzymatic activity, is found about 5.2 Å from one iron of the iron-oxygen cluster in the E. coli enzyme (6). A weak magnetic coupling exists between the tyrosyl radical and the iron-oxygen cluster (5, 9 -12). Model building studies of the R1⅐R2 complex suggest that the radical/iron clusters in the E. coli RNR-R2 are about 35 Å from the substrate binding active site in protein R1 (8). Class I RNR can be further divided into categories a and b based on sequence homologies (13). Although eukaryotes belong to class Ia along with the E. coli RNR, a number of prokaryotes belong to class Ib. The X-band EPR spectra of the tyrosyl radical of class Ia proteins are all similar to that of the E. coli RNR-R2. In a class Ib enzyme on the other hand, the EPR spectrum of the RNR tyrosyl radical of the Salmonella typhimurium R2F protein is strikingly similar to that observed for the Y D ⅐ tyrosyl radical of PSII (12, 13). This difference between several class Ia enzymes and the class Ib enzyme is due to a different dihedral angle arrangement for the ␤-protons relative to the ring of the tyrosyl radical in the two groups, whereas the spin density d...

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“…In order to get more information on the nature of the lowest lying spin states electron paramagnetic resonance (EPR) spectra were recorded on a laboratory made high field-high frequency spectrometer [19]. The use of a high field has been chosen to enhance the accuracy in the determination of the g factor.…”

Section: Magnetic Properties Of Cr 8 Nimentioning

confidence: 99%

Spin frustration effects in an odd-member antiferromagnetic ring and the magnetic Möbius strip

Cador

Gatteschi

Sessoli

et al. 2005

Journal of Magnetism and Magnetic Materials

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The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=3/2 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Möbius strip. The "knot" of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site.

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EPR spectroscopy at very high field

Cited by 141 publications

References 6 publications

Restoring Proper Radical Generation by Azide Binding to the Iron Site of the E238A Mutant R2 Protein of Ribonucleotide Reductase fromEscherichia coli

Restoring Proper Radical Generation by Azide Binding to the Iron Site of the E238A Mutant R2 Protein of Ribonucleotide Reductase fromEscherichia coli

High Field EPR Studies of Mouse Ribonucleotide Reductase Indicate Hydrogen Bonding of the Tyrosyl Radical

Spin frustration effects in an odd-member antiferromagnetic ring and the magnetic Möbius strip

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