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  • Title: A new species of bound ubisemiquinone anion in QH2: cytochrome c oxidoreductase.
    Author: de Vries S, Albracht SP, Berden JA, Slater EC.
    Journal: J Biol Chem; 1981 Dec 10; 256(23):11996-8. PubMed ID: 6271770.
    Abstract:
    Using a combination of EPR and low temperature diffuse reflectance spectroscopy, a new species of semiquinone anion has been detected in QH2:cytochrome c oxidoreductase in submitochondrial particles under conditions of oxidant-induced extra reduction of cytochrome b. In contrast to the previously detected semiquinone anion, this new species is insensitive to antimycin but sensitive to treatment with 2,3-dimercaptopropanol and O2. The two species can easily be distinguished on the basis of their respective EPR properties since they differ in g-value, line width, and microwave power saturation behavior. It is concluded that the two species of semiquinone anion are bound to different domains on QH2:cytochrome c oxidoreductase. The existence of two different semiquinone anions in the enzyme strongly supports a mechanism of electron flow as proposed in the Q-cycle.
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