Fig. 1.

CoQ role in the mitochondrial electron transport chain (mtETC). Schematic representation of the respiratory chain status (electron flow and proton pumping activities) in wild-type (ρ⁺) cells (A), mtDNA-less (ρ°) cells (B), and in cells with knockout mutations in either complex I (C) or in complexes III or IV (D). The pivotal role of CoQ as electron acceptor from different routes and as electron donor to complexes III and IV is highlighted. DHODH, dihydroorotate dehydrogenase; G3PDH, glycerol-3-phosphate dehydrogenase (glycerol-phosphate shuttle); SDH, succinate dehydrogenase; ETF-QO, electron-transfer flavoprotein-ubiquinone oxidoreductase; TCA, tricarboxylic acid cycle.