Characterization of the iron-sulfur centers in succinate dehydrogenase.

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Abstract
Two techniques were applied to the determination of the number and type (2-Fe, 4-Fe) of Fe-S centers in the [mammalian] Fe-S flavoprotein succinate dehydrogenase [succinate:(acceptor)oxidoreductase, EC 1.3.99.1]. One procedure uses p-CF3C6H4SH as an extrusion reagent and Fourier transform 19F NMR as the method of detection and quantitation of extruded cores of these centers in the form of [Fe2S2(SRF)4]2- and [Fe4S4(SRF)4]2- (RF = p-C6H4CF3). The 2nd procedure, interprotein core transfer, involves thiol displacement of Fe-S cores followed by specific core transfer to the apoproteins of Bacillus polymyxa ferredoxin and [adrenal cortex] adrenodoxin. Detection and quantitation are accomplished by EPR of reduced proteins at low temperatures. Both procedures clearly show that succinate dehydrogenase contains 2 dimeric (Fe2S2) and 1 tetrameric (Fe4S4) centers/mol of histidyl flavin, accounting for all 8 nonheme Fe and 8 labile S atoms found by chemical analysis. The results remove uncertainties created by the less than stoichiometric amounts of binuclear centers detected by EPR after dithionite reduction and provide secure characterization of the Fe-S centers in this enzyme.