ELECTRON SPIN-ECHO ENVELOPE MODULATION AND SPIN SPIN INTERACTION STUDIES OF THE IRON SULFUR CLUSTERS IN FUMARATE REDUCTASE OF ESCHERICHIA-COLI

Electron spin-echo envelope modulation (ESEEM) spectroscopy has been performed in order to obtain strucutral information about the reduced [2Fe-2S], [4Fe-4S] and oxidized [3Fe-4S] clusters in purified fumarate reductase from Escherichia coli. Spin echoes were detected from the reduced iron-sulphur clusters (centres 1-3) and also from oxidized centre 3. The ESEEM studies showed that the reduced [2Fe-2S] cluster is coordinated by a peptide N-14. In this study, we also observed a weak interaction between the oxidized [3Fe-4S] cluster and a peptide N-14; there was no evidence for coordination to the N-14-atoms of imidazole rings. Spin-lattice and spin-spin relaxation rates for oxidized and reduced protein were measured, and the results confirmed the presence of a spin-spin interaction between reduced centres 1 and 2.