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  • Title: Stabilized ubisemiquinone in reconstituted succinate ubiquinone reductase.
    Author: Xu Y, Salerno JC, Wei YH, King TE.
    Journal: Biochem Biophys Res Commun; 1987 Apr 14; 144(1):315-22. PubMed ID: 3034247.
    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.
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