Properties of the S-3 iron-sulphur centre of succinate dehydrogenase in the intact respiratory chain of beef heart mitochondria

Abstract

; this new species is paramagnetic in the oxidised form as are the bacterial high potential iron-sulphur proteins (Hipip [2]). This new iron-sulphur protein exhibits an EPR signal centred at g = 2.01 with a peak to peak width of approximately 25 gauss. A similar EPR signal was detected in the succinate-ubiquinone (UQ) reductase (Complex II [3]), in an equimolar concentration to that of flavin [4]. This signal was, however, not initially detected [4] in the succinate dehydrogenase (SDH) preparation, which contained the same content of non-haem iron and acid labile sulphide per flavin as Complex II, but was not reconstitutively active. Subsequently this Hipip-type iron-sulphur centre was found to become extremely labile towards oxygen upon removal of the dehydro- genase from the mitochondrial membrane. Thus, resonance absorbance of a Hipip-type iron-sulphur centre is detectable only in the reconstitutively active SDH preparation [.5]. This Hipip-type iron- sulphur centre, present in the succinate dehydro- genase, was designated as Centre S-3, following Centres S-l and S-2 (two ferredoxin type iron-sulphur centres previously identified in the succinate dehy- drogenase [ 51). More recently it has been shown that intact mitochondria contain two different ‘Hipip’type species (paramagnetic in the oxidised form); these species can be distinguished by their temperature and micropower saturation profiles and the absence of one of the species from sub-mitochon- drial particle preparations [6]. Of the two ‘Hipip’ species only that which is present in submitochondrial