Fig. 1.

Mitochondrial respiratory chain and alternative enzymes. Schematic representation of the canonical mitochondrial respiratory chain (in black and white) characterized by four multi-subunit complexes (Complex I, Complex II, Complex III and Complex IV) and two intermediary substrates (ubiquinone and cytochrome c) generating an electrochemical gradient through the inner mitochondrial membrane. Protons flow back to the matrix via Complex V to produce ATP. The figure also illustrates alternative pathways of NAD(P)H and ubiquinol oxidation (in green) represented by alternative dehydrogenases (NDH2) and alternative oxidases (AOX), respectively. CI to CV, complexes I to V; UQ, ubiquinone; UQH2, ubiquinol; Cyt c, cytochrome c; MIMS, mitochondrial intermembrane space