A new species of bound ubisemiquinone anion in QH2: cytochrome c oxidoreductase

• Published in: The Journal of biological chemistry Vol. 256; no. 23; pp. 11996 - 11998
• Main Authors: de Vries, S, Albracht, S P, Berden, J A, Slater, E C
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 10-12-1981
• Subjects: Animals; Cattle; Coenzymes; Cytochrome c Group - metabolism; Electron Spin Resonance Spectroscopy; Electron Transport Complex III; Kinetics; Mitochondria - enzymology; Mitochondria, Heart - enzymology; Multienzyme Complexes - metabolism; NADH, NADPH Oxidoreductases - metabolism; Protein Binding; Quinone Reductases - metabolism; Submitochondrial Particles - enzymology; Ubiquinone - analogs & derivatives; Ubiquinone - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)43222-x

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.