Domain movement of iron sulfur protein in cytochrome bc1 complex is facilitated by the electron transfer from cytochrome bL to bH

The key step of the "protonmotive Q-cycle" mechanism for cytochrome bc(1) complex is the bifurcated oxidation of ubiquinol at the Qp site. ISP is reduced when its head domain is at the b-position and subsequent move to the c(1) position, to reduce cytochrome c(1), upon protein conformational changes caused by the electron transfer from cytochrome b(L) to b(H). Results of analyses of the inhibitory efficacy and the binding affinity, determined by isothermal titration calorimetry, of Pm and Pf, on different redox states of cytochrome bc(1) complexes, confirm this speculation. Pm inhibitor has a higher affinity and better efficacy with the cytochrome b(H) reduced complex and Pf binds better and has a higher efficacy with the ISP reduced complex. (C) 2008 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.