Mammalian versus yeast OXPHOS system. Mammalian versus yeast OXPHOS system. The figure shows the main enzymatic systems involved in mitochondrial oxidative phosphorylation (OXPHOS) in yeast and mammals. In mammals (top), complexes I-IV together with ubiquinone (Q) and cytochrome c (cyt c) transfer electrons to oxygen from the NADH and succinate produced by the Krebs cycle. These transfers are, at the level of complexes I, III and IV, coupled to proton translocation from the matrix into the intermembrane space (IMS). The resulting proton gradient across the inner mitochondrial membrane (IM) is used by complex V (F1Fo ATP synthase) to produce ATP from ADP and inorganic phosphate (Pi). Part of the ATP produced in the matrix is exchanged against cytosolic ADP by the ADP/ATP translocase (ANT) to provide the whole cell with energy and to maintain the ADP phosphorylation capacity of mitochondria. The OXPHOS system of S. cerevisiae (bottom) is highly similar to the mammalian system except that complex I is replaced by a non-proton-translocating NADH dehydrogenase (Ndi1p) at the inner side of the IM. There are also in S. cerevisiae two NADH dehydrogenases on the external side of the IM (Nde1p, Nde2p) that deliver electrons at the level of ubiquinone. The protein structures are from the Protein Data Bank (PDB) and are at the same scale (indicated by the scale bar). Jean-Paul Lasserre et al. Dis. Model. Mech. 2015;8:509-526 © 2015. Published by The Company of Biologists Ltd