ISSN:
1432-1327
Keywords:
High-potential iron protein IEctothiorhodospira halophila
;
Mössbauer
;
Electron paramagnetic resonance
;
57Fe electron-nuclear double resonance
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
4 S4]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 Mössbauer 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 Mössbauer 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 Mössbauer 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 Mössbauer 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 Mössbauer 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 Mössbauer spectrum, indicating a mixed-valence state of Fe2.5 + for each.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050345
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