New method for the spin quantitation of [4Fe-4S](+) clusters with S = (3)/(2). Application to the FS0 center of the NarGHI nitrate reductase from Escherichia coli.
In conventional analyses of g approximately 5 signals given by [4Fe-4S](+) clusters with S = 3/2, the effective g values that cannot be measured in the electron paramagnetic resonance (EPR) spectrum are deduced from rhombograms calculated by assuming that the g matrix is isotropic with g(x) = g(y) = g(z) = 2.00. We have shown that when the two low-field peaks corresponding to the Kramers doublets are visible in the spectrum, a new, independent piece of information about the system can be obtained by studying the temperature dependence of the ratio of the area under these peaks. By applying this method to the g approximately 5 signals displayed by NarGHI nitrate reductase, we were able to determine all the parameters of the spin Hamiltonian of FS0 centers with S = 3/2 and to measure accurately their number. Our results indicate that simple analyses based on the assumption of an isotropic g matrix can give rise to very large errors.
Lanciano
Pascal
P
Unité de Bioénergétique et Ingénierie des Protéines (UPR9036), Institut de Biologie Structurale et de Microbiologie, CNRS, Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Savoyant
Adrien
A
Grimaldi
Stéphane
S
Magalon
Axel
A
Guigliarelli
Bruno
B
Bertrand
Patrick
P
D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D050901:Nitrate Reductase / Q000737:chemistry*; D010084:Oxidation-Reduction; D011199:Potentiometry; D013696:Temperature
D007506:Iron-Sulfur Proteins; D050901:Nitrate Reductase