Mossbauer spectra of the oxidized [Fe4S4]3+ and the reduced [Fe4S4]2+ clusters in the high-potential iron protein I from Ectothiorhodospira halophila were measured in a temperature range from 5 K to 240 K. EPR measurements and 57Fe electron-nuclear double resonance (ENDOR) experiments were carried out with the oxidized protein. In the oxidized state the cluster has a net spin S = 1/2 and is paramagnetic. As common in [Fe4S4]3+ clusters, the Mossbauer spectrum was simulated with two species contributing equally to the absorption area: two Fe3+ atoms couple to the 'ferric-ferric' pair, and one Fe2+ and one Fe3+ atom give the 'ferric- ferrous pair'. For the simulation of the Mossbauer spectrum, g-values were taken from EPR measurements. A-tensor components were determined by 57Fe ENDOR experiments that turned out to be a necessary source of estimating parameters independently. In order to obtain a detailed agreement of Mossbauer and ENDOR data, electronic relaxation has to be taken into account. Relaxing the symmetry condition in a way that the electric field gradient tensor does not coincide with g- and A-tensors yielded an even better agreement of experimental and theoretical Mossbauer spectra. Spin-spin and spin-lattice relaxation times were estimated by pulsed EPR; the former turned out to be the dominating mechanism at T=5 K. Relaxation times measured by pulsed EPR and obtained from the Mossbauer fit were compared and yield nearly identical values. The reduced cluster has one additional electron and has a diamagnetic (S=0) ground state. All the four irons are indistinguishable in the Mossbauer spectrum, indicating a mixed-valence state of Fe25+ for each.

Simultaneous interpretation of Mössbauer, EPR and 57Fe ENDOR spectra of the [Fe4S4] cluster in the high-potential iron protein I Ectothiorhodospira halophila / BERTINI I; DILG A.W.E; IAKOVLEVA O; C. LUCHINAT; MINCIONE G; PARAK F. - In: JBIC. - ISSN 0949-8257. - STAMPA. - 4:(1999), pp. 727-741. [10.1007/s007750050345]

Simultaneous interpretation of Mössbauer, EPR and 57Fe ENDOR spectra of the [Fe4S4] cluster in the high-potential iron protein I Ectothiorhodospira halophila

BERTINI, IVANO;LUCHINAT, CLAUDIO;
1999

Abstract

Mossbauer spectra of the oxidized [Fe4S4]3+ and the reduced [Fe4S4]2+ clusters in the high-potential iron protein I from Ectothiorhodospira halophila were measured in a temperature range from 5 K to 240 K. EPR measurements and 57Fe electron-nuclear double resonance (ENDOR) experiments were carried out with the oxidized protein. In the oxidized state the cluster has a net spin S = 1/2 and is paramagnetic. As common in [Fe4S4]3+ clusters, the Mossbauer spectrum was simulated with two species contributing equally to the absorption area: two Fe3+ atoms couple to the 'ferric-ferric' pair, and one Fe2+ and one Fe3+ atom give the 'ferric- ferrous pair'. For the simulation of the Mossbauer spectrum, g-values were taken from EPR measurements. A-tensor components were determined by 57Fe ENDOR experiments that turned out to be a necessary source of estimating parameters independently. In order to obtain a detailed agreement of Mossbauer and ENDOR data, electronic relaxation has to be taken into account. Relaxing the symmetry condition in a way that the electric field gradient tensor does not coincide with g- and A-tensors yielded an even better agreement of experimental and theoretical Mossbauer spectra. Spin-spin and spin-lattice relaxation times were estimated by pulsed EPR; the former turned out to be the dominating mechanism at T=5 K. Relaxation times measured by pulsed EPR and obtained from the Mossbauer fit were compared and yield nearly identical values. The reduced cluster has one additional electron and has a diamagnetic (S=0) ground state. All the four irons are indistinguishable in the Mossbauer spectrum, indicating a mixed-valence state of Fe25+ for each.
1999
4
727
741
BERTINI I; DILG A.W.E; IAKOVLEVA O; C. LUCHINAT; MINCIONE G; PARAK F
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/212250
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