48] EPR and other properties of succinate dehydrogenase

Abstract

This chapter provides information on electron paramagnetic resonance (EPR) and other properties of succinate dehydrogenase. EPR characteristics of iron–sulfur centers in reconstitutively active and inactive succinate dehydrogenase preparations are also summarized in the chapter. Three distinct iron–sulfur centers (clusters) and flavin free radicals are identified in the succinate dehydrogenase using EPR spectroscopy under various conditions. Two iron–sulfur centers show EPR signals in the reduced state, similar to plant or bacterial ferredoxins (Fd); the third center is paramagnetic in the oxidized state, as in case of Chromatium high-potential iron–sulfur protein (HiPIP). EPR signals of the HiPIP-type center (designated center S-3) are readily detectable in particulate succinate-Q reductase. The temperature affects the spectra of iron–sulfur centers in three major ways by decreasing the linewidth. At low temperatures, however, the signal may saturate at low power levels, decreasing the maximum intensity obtainable. Therefore it is necessary to examine power dependence of the signal at different temperatures.