title: Stabilized ubisemiquinone in reconstituted succinate ubiquinone reductase.
abstract: QP-S, a ubiquinone (Q) protein, accepts electrons from succinate through succinate dehydrogenase (SDH). A new method has produced a preparation of QP-S which has a different amino acid composition and SDS gel electrophoretic pattern from that of the old preparation (Biochemistry 19, 3579-3585 (1980)). The new preparation contains less than 1 nmol heme/mg protein; the activity of the preparation was not proportional to its heme content. A thenoyltrifluoroacetone sensitive free radical signal was detected by EPR spectroscopy in succinate-Q reductase reconstituted from this QP-S and SDH; the characteristics of this species identify it as ubisemiquinone. At pH 7.4, the Em of the two electron step was about 70 mV with E1 = 5 mV and E2 = 125 mV. The properties of the radical differed slightly from those of "Qs" radical in more intact preparations (e.g. submitochondrial particles). The present is the simplest system in which such a succinate reducible ubisemiquinone free radical has been demonstrated.
mesh_terms: D003067:Coenzymes; D004578:Electron Spin Resonance Spectroscopy; D042963:Electron Transport Complex II; D005609:Free Radicals; D009097:Multienzyme Complexes; D010088:Oxidoreductases; D013385:Succinate Dehydrogenase; D013804:Thenoyltrifluoroacetone; D014451:Ubiquinone / Q000031:analogs & derivatives*
chemical_list: D003067:Coenzymes; D005609:Free Radicals; D009097:Multienzyme Complexes; D014451:Ubiquinone; D013804:Thenoyltrifluoroacetone; D010088:Oxidoreductases; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; C024989:coenzyme Q10