Design and use of photoactive ruthenium complexes to study electron transfer within cytochrome bc(1) and from cytochrome bc(1) to cytochrome c
by Millett, Francis Spencer; Havens, Jeffrey Allen; Rajagukguk, Sany Clean Johnson; Durham, Bill
The cytochrome bc(1) complex (ubiquinone:cytochrome c oxidoreductase) is the central integral membrane protein in the mitochondrial respiratory chain as well as the electron-transfer chains of many respiratory and photosynthetic prokaryotes. Based on X-ray crystallographic studies of cytochrome bc(1), a mechanism has been proposed in which the extrinsic domain of the iron-sulfur protein first binds to cytochrome b where it accepts an electron from ubiquinol in the Q(o) site, and then rotates by 57 degrees to a position close to cytochrome c(1) where it transfers an electron to cytochrome c(1). This review describes the development of a ruthenium photooxidation technique to measure key electron transfer steps in cytochrome bc(1), including rapid electron transfer from the iron-sulfur protein to cytochrome c(1). It was discovered that this reaction is rate-limited by the rotational dynamics of the iron-sulfur protein rather than true electron transfer. A conformational linkage between the occupant of the Q(o) ubiquinol binding site and the rotational dynamics of the iron-sulfur protein was discovered which could play a role in the bifurcated oxidation of ubiquinol. A ruthenium photoexcitation method is also described for the measurement of electron transfer from cytochrome c(1) to cytochrome c. This article is part of a Special Issue entitled: Respiratory Complex III and related bc complexes. (C) 2012 Elsevier B.V. All rights reserved.
- Biochimica et Biophysica Acta-Bioenergetics
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