Schematic structure of mitochondrial complexes II and III indicating the main amino acids of the different subunits involved in binding of inhibitors and in resistance. Complex II contains four subunits, whereas complex III consists of 10 to 11 polypeptides. For complex III, only three main subunits (i.e., Cytb, cytochrome b; ISP Rieske, iron sulfur protein with a Rieske-type cluster; cytc1, cytochrome c 1 ) directly involved in the electron transfer are shown. The amino acids involved in the binding of substrates (i.e., ubiquinone or ubiquinol) or of inhibitors were identified in crystallographic studies involving complex II or III from various origins (20, 28, 33, 35, 36, 59, 75). Amino acids are numbered according to B. cinerea sequences.