Domain movement of iron sulfur protein in cytochrome bc 1 complex is facilitated by the electron transfer from cytochrome b L to b H

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.