The reverse shift of the EPR line of paramagnetic centers coupled to species with a fast paramagnetic relaxation

Salikhov, K. M.; Galeev, R. T.; Воронкова, В. К.; Yablokov, Yu. V.; Legendziewicz, J.

doi:10.1007/bf03161855

Cited by 21 publications

(22 citation statements)

References 2 publications

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“…38 The results of this simulation as a function of the relaxation time T 1 of the faster relaxing center is shown in Figure 8B. Details of the model employed in the simulation are given in ref 20, and the dependence with temperature of The double-headed arrows connect microstates separated by one-electron reduction/oxidation (P 0 and P 11 represent the fully oxidized and reduced states, respectively) (b) EPR spectrum of Da Aor samples at -450 and -334 mV.…”

Section: Assignment Of the Epr Active Centers With Those Seen In The mentioning

confidence: 99%

Structural and Electron Paramagnetic Resonance (EPR) Studies of Mononuclear Molybdenum Enzymes from Sulfate-Reducing Bacteria

et al. 2006

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Molybdenum and tungsten are found in biological systems in a mononuclear form in the active site of a diverse group of enzymes that generally catalyze oxygen-atom-transfer reactions. The metal atom (Mo or W) is coordinated to one or two pyranopterin molecules and to a variable number of ligands such as oxygen (oxo, hydroxo, water, serine, aspartic acid), sulfur (cysteines), and selenium (selenocysteines) atoms. In addition, these proteins contain redox cofactors such as iron-sulfur clusters and heme groups. All of these metal cofactors are along an electron-transfer pathway that mediates the electron exchange between substrate and an external electron acceptor (for oxidative reactions) or donor (for reductive reactions). We describe in this Account a combination of structural and electronic paramagnetic resonance studies that were used to reveal distinct aspects of these enzymes. Mononuclear Molybdenum Enzymes: Classification and General PropertiesMolybdenum and tungsten are found in biological systems in a mononuclear form in the active site of a diverse group of enzymes that generally catalyze oxygen-atom-transfer reactions. 1,2 Mononuclear molybdenum-containing enzymes are ubiquitous and participate in several biological processes occurring in nature, such as denitrification, the greenhouse effect, and pollution of the water soil. 3,4,5 Mononuclear molybdenum enzymes have been divided into three groups called the xanthine oxidase (XO), dimethyl sulfoxide reductase (DMSOR), and sulfite oxidase (SO) families. 1,6 These three families include not only the enzymes that give the name to the different groups but also diverse enzymes, such as aldehyde oxidoreductases, nitrate reductases, and formate dehydrogenases, among others. The active site of these enzymes (Figure 1a) includes the metal atom coordinated to one or two pyranopterin molecules and to a variable number of ligands such as oxygen (oxo, hydroxo, water, serine, aspartic acid), sulfur (cysteines), and selenium (selenocysteines) atoms. The pyranopterin molecule is an organic ligand that can be either in the monophosphate form or have a nucleotide molecule attached by a pyrophosphate link (Figure 1b). 7 In addition, these proteins may also have other redox cofactors such as iron-sulfur (FeS) centers, hemes, and flavin groups, which are involved in intra-and intermolecular electron-transfer processes. A tungstencontaining aldehyde oxidoreductase from Pyrococcus furiosus presents a similar active-site structure and has been classified in a different family. 2 However, other tungsten enzymes such as the formate dehydrogenase from Desulfovibrio gigas belong to the DMSOR family, being closely related to the corresponding molybdenum enzymes. 8 With a few exceptions, these enzymes catalyze the transfer of an oxygen atom from water to the product (or vice versa) in reactions that imply a net exchange of two electrons between the enzyme and substrate and in which the metal ion cycles between the redox states IV and VI. Figure 2 shows two representative exam...

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Section: Assignment Of the Epr Active Centers With Those Seen In The mentioning

confidence: 99%

Structural and Electron Paramagnetic Resonance (EPR) Studies of Mononuclear Molybdenum Enzymes from Sulfate-Reducing Bacteria

et al. 2006

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“…The temperature variation of the spectra associated with Mo(V) species were simulated using a home-made program based on the formalism WBR (Wangenesst, Bloch, and Redfield) for a dimer of two S=1/2 ions [19]. This program solves the components of the density matrix required to calculate the imaginary part of v¢¢(x) (dynamic susceptibility) and takes the elements of the relaxation matrix as semi-empirical parameters (T 1 and T 2 ) for each center [20].…”

Section: Spectroscopic Methodsmentioning

confidence: 99%

“…Therefore, the (Fig. 3) were simulated by assuming a dimeric model composed of two interacting S=1/2 centers relaxing independently [20], including in addition the hyperfine coupling with a nucleus of nuclear spin I=1/2 at one of the centers, both centers being magnetically coupled only by exchange interaction (Fig. 3).…”

Section: Analysis Of the Magnetic Interactionsmentioning

confidence: 99%

Incorporation of either molybdenum or tungsten into formate dehydrogenase from Desulfovibrio alaskensis NCIMB 13491; EPR assignment of the proximal iron-sulfur cluster to the pterin cofactor in formate dehydrogenases from sulfate-reducing bacteria

et al. 2003

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We report the characterization of the molecular properties and EPR studies of a new formate dehydrogenase (FDH) from the sulfate-reducing organism Desulfovibrio alaskensis NCIMB 13491. FDHs are enzymes that catalyze the two-electron oxidation of formate to carbon dioxide in several aerobic and anaerobic organisms. D. alaskensis FDH is a heterodimeric protein with a molecular weight of 126±2 kDa composed of two subunits, a=93±3 kDa and b=32±2 kDa, which contains 6±1 Fe/molecule, 0.4±0.1 Mo/molecule, 0.3±0.1 W/molecule, and 1.3±0.1 guanine monophosphate nucleotides. The UV-vis absorption spectrum of D. alaskensis FDH is typical of an iron-sulfur protein with a broad band around 400 nm. Variable-temperature EPR studies performed on reduced samples of D. alaskensis FDH showed the presence of signals associated with the different paramagnetic centers of D. alaskensis FDH. Three rhombic signals having g-values and relaxation behavior characteristic of [4Fe-4S] clusters were observed in the 5-40 K temperature range. Two EPR signals with all the g-values less than two, which accounted for less than 0.1 spin/protein, typical of mononuclear Mo(V) and W(V), respectively, were observed. The signal associated with the W(V) ion has a larger deviation from the free electron g-value, as expected for tungsten in a d 1 configuration, albeit with an unusual relaxation behavior. The EPR parameters of the Mo(V) signal are within the range of values typically found for the slow-type signal observed in several Mo-containing proteins belonging to the xanthine oxidase family of enzymes. Mo(V) resonances are split at temperatures below 50 K by magnetic coupling with one of the Fe/S clusters. The analysis of the inter-center magnetic interaction allowed us to assign the EPR-distinguishable iron-sulfur clusters with those seen in the crystal structure of a homologous enzyme.

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“…The EPR spectra show that the lifetime of spins in a definite state determines also the exchange interactions between ions with extremely different spin-lattice relaxation times [6,11]. For example, for T1 '(Nd) 10" s -' only very rapid exchange might exist.…”

Section: Introductionmentioning

confidence: 99%

“…The analysis of the EPR line shape at low temperatures allowed us to evaluate J cu -Na 0.4 cm-' [11].…”

Section: Introductionmentioning

confidence: 99%

Formation of correlated spin systems in one- and two-dimensional copper and lanthanide compounds

et al. 2000

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Electron paramagnetic resonance (EPR) of the systems of exchange-coupled ions differing strongly by spin-lattice relaxation times are discussed. The physical description of a rapid process which modulates and averages out the other, more slow one, is extended to the situations when paramagnetic ions participate in several exchange processes. The layered copper-neodymium squarate, [CuNd2(C404)4H20 16] • 2H20 (I), and the one-dimensional copper-lanthanide C1 3 -acetates, CuLn2 X (Cl3 000O)8 .6H20 (Ln = Nd3 + (II), Pr3 + (III)), were investigated by X-band EPR in the temperature range 4.2-300 K. These compounds were shown to consist of subunits admitting exchange interaction between Cu ions, Cu-Nd ions and Nd-Nd ions. At high temperatures the short spin-lattice relaxation time of Nd3 + averages out the Cu-Nd exchange interaction. The manifestation of this interaction should be temperature dependent when governed by the spin-lattice relaxation of one of the partners. The collective Cu spin-system exists in I at T> 250 K (Jc" c" = 0.1 cm-') and gradually transforms into Cu-Nd spin-system which dominates at T < 20-30 K (JcNd 0.4 cm-') with Jcu-Na > Jc,-cu > JNd-Na' Polymer chains in II may be considered as weakly interacting asymmetrical triads -Nd,-Cu-Nd 2 -(with the largest components of J,, tensor -0.3 cm -'). For III the lowest state of Pr" was proved to be a nonmagnetic singlet with JCu_er equal to zero. Very weak, temperature-dependent exchange interaction between Cue ions via two Pr3 + ions (J 0.015 cm-' at T= 4.2 K) was observed.

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The reverse shift of the EPR line of paramagnetic centers coupled to species with a fast paramagnetic relaxation

Cited by 21 publications

References 2 publications

Structural and Electron Paramagnetic Resonance (EPR) Studies of Mononuclear Molybdenum Enzymes from Sulfate-Reducing Bacteria

Structural and Electron Paramagnetic Resonance (EPR) Studies of Mononuclear Molybdenum Enzymes from Sulfate-Reducing Bacteria

Incorporation of either molybdenum or tungsten into formate dehydrogenase from Desulfovibrio alaskensis NCIMB 13491; EPR assignment of the proximal iron-sulfur cluster to the pterin cofactor in formate dehydrogenases from sulfate-reducing bacteria

Formation of correlated spin systems in one- and two-dimensional copper and lanthanide compounds

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