Characterization of ubisemiquinone radicals in succinate-ubiquinone reductase.
A thenoyl trifluoroacetone-sensitive and antimycin-insensitive ubisemiquinone radical (Qs) is readily detected in purified succinate-cytochrome c reductase. When this reductase is resolved into succinate-Q and ubiquinol-cytochrome c reductases, Qs was not detected in either reductase. The difficulty in detecting such a radical in purified succinate-Q reductase has puzzled investigators for years. A deficiency of Q in the isolated complex is the reason for the failure to detect Qs. Upon addition of exogenous Q, a thenoyl trifluoroacetone-sensitive Q-radical is readily detectable in isolated succinate-Q reductase under a controlled redox potential. Maximum radical concentration is observed when 5 mol of exogenous Q, per mole of flavin, is added. The radical gives an EPR signal with a g-value of 2.005 and a line-width of 12 G. The Em of Qs is 84 mV at pH 7.4, with half-potentials of E1 = 40 mV and E2 = 128 mV. The Qs-radical does not show power saturation, even at 200 mW.
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Department of Biochemistry, Oklahoma State University, Stillwater 74078.
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D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D003067:Coenzymes; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005609:Free Radicals; D066298:In Vitro Techniques; D008928:Mitochondria / Q000201:enzymology; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000737:chemistry; D010084:Oxidation-Reduction; D013384:Succinate Cytochrome c Oxidoreductase / Q000737:chemistry*; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000737:chemistry
D003067:Coenzymes; D005609:Free Radicals; D009097:Multienzyme Complexes; C032456:antimycin; D014451:Ubiquinone; D000968:Antimycin A; D013384:Succinate Cytochrome c Oxidoreductase; C024989:coenzyme Q10