NDLI: On the Mechanism of Quinol Oxidation in thebc 1 Complex

Content Provider	Journal of Biological Chemistry (JBC)
Author	Jünemann, Susanne Heathcote, Peter Rich, Peter R.
Description	Qo sites, the quinone reduction/proton Input and quinol oxidation/proton Output sites of thebc1 complex, respectively (Qi) The high and low potential hemes of cytochrome b, also termed b-562 andb-566 from their reduced α-band maximum, respectively (hemes bH and bL)
Abstract	The question of whether significant levels of a semiquinone can be generated in the Qo site of thebc 1 complex under conditions of oxidant-induced reduction is relevant to the mechanism of bifurcation of electron transfer in this site. It has already been reported that beef heart submitochondrial particles under such conditions exhibit an EPR-detectable semiquinone, which is distinct from Q⨪i and which was attributed to a semiquinone in the Qo site (de Vries, S., Albracht, S. P. J., Berden, J. A., and Slater, E. C. (1981) J. Biol. Chem. 256, 11996–11998). However, we show here that this signal, which can be generated to a level of around 0.1 perbc 1 monomer, is insensitive to the Qo site inhibitors myxothiazol, E-β-methoxyacrylate-stilbene, and stigmatellin, indicating that it does not arise from a Q⨪o species. Based on sensitivities to inhibitors of other Q sites, up to 60% of the signal may arise from semiquinones of complexes I and II. We further show that the iron-sulfur center remains EPR silent under oxidant-induced reduction conditions. Overall, the results indicate that, under conditions of oxidant-induced reduction, the Qo site is occupied primarily by quinol with the iron-sulfur center oxidized, or, possibly, by an antiferromagnetically coupled semiquinone/reduced iron-sulfur center pair, which are EPR silent. This is discussed in relation to proposed mechanisms of quinol oxidation in the Qo site, and we describe a minimal intermediate-controlled bifurcation model based on rate constants by which bifurcated electron transfer at the Qo site might occur.
Related Links	http://www.jbc.org/content/273/34/21603.abstract
Ending Page	21607
Starting Page	21603
Page Count	5
File Format	HTM / HTML PDF
ISSN	00219258
Journal	Journal of Biological Chemistry (JBC)
Issue Number	34
Volume Number	273
DOI	10.1074/jbc.273.34.21603
e-ISSN	1083351X
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	1998-08-21
Access Restriction	Open
Subject Keyword	British Anti-Lewisite, 2,3-dimercaptoethanol (BAL) E-β-methoxyacrylate. (MOA) MEMBRANES AND BIOENERGETICS
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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