title: Detection of a tetranuclear iron-sulfur center in fumarate reductase from Escherichia coli by electron paramagnetic resonance spectroscopy.
abstract: Soluble fumarate reductase and fumarate reductase complex from Escherichia coli have been investigated by electron paramagnetic resonance spectroscopy. Both succinate- and dithionite-reduced samples show signals associated with a [2Fe-2S]1+ cluster that account maximally for slightly more than one spin/molecule. In addition, at temperatures below 20 K, dithionite-reduced samples exhibit broad and complex features, to high and low field of the [2Fe-2S]1+ signal, that are attributable to a spin coupled [4Fe-4S]1+ cluster. Preliminary attempts to quantify the signals indicate that the [4Fe-4S] cluster is present in an approximate 1:1 stoichiometry with the [2Fe-2S] cluster. The observed enhancement of the spin relaxation of the [2Fe-2S]1+ cluster on dithionite reduction is attributed to spin-spin interaction between the S = 1/2, reduced tetranuclear and binuclear clusters.
mesh_terms: D004227:Dithionite; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D010084:Oxidation-Reduction; D013385:Succinate Dehydrogenase; D013386:Succinates; D019802:Succinic Acid
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D013386:Succinates; D004227:Dithionite; D019802:Succinic Acid; D013385:Succinate Dehydrogenase