Design and use of photoactive ruthenium complexes to study electron transfer within cytochrome bc1 and from cytochrome bc1 to cytochrome c

The cytochrome bc1 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 bc1, 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 Qo site, and then rotates by 57° to a position close to cytochrome c1 where it transfers an electron to cytochrome c1. This review describes the development of a ruthenium photooxidation technique to measure key electron transfer steps in cytochrome bc1, including rapid electron transfer from the iron–sulfur protein to cytochrome c1. 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 Qo 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 c1 to cytochrome c. This article is part of a Special Issue entitled: Respiratory Complex III and related bc complexes.

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► Photoactive ruthenium complexes to study electron transfer in the cytochrome bc1 complex
► Electron transfer from the iron–sulfur protein to cytochrome c1
► Dynamics of rotation of the iron–sulfur protein from the b state to the c1 state
► A conformational linkage between Qo site and of the iron–sulfur protein
► Electron transfer from cytochrome c1 to cytochrome c