EXPERIMENTAL FIGURE 12-26 Electrophoresis and electron microscopic imaging have identified an electron-transport chain supercomplex containing complexes I, III, and IV. (a) Membrane proteins in isolated bovine heart mitochondria were solubilized with a detergent, and the complexes and supercomplexes were separated by gel electrophoresis using the blue native (BN)-PAGE method. Each blue-stained band within the gel represents the indicated protein complex or supercomplex. The intensity of the blue stain is approximately proportional to the amount of complex or supercomplex present. (b) Supercomplex I/III₂/IV was extracted from a BN-PAGE gel, frozen, and visualized by cryoelectron tomography. The left image shows the three-dimensional surface structure viewed from an orientation parallel to the presumptive plane of the membrane. The right image is the same structure into which were fit models of the structures of the individual complexes: complex I (blue), dimer of complex III (III₂, orange), and complex IV (green). Colored dashed lines represent the approximate outlines of these complexes. The complex I structure is based on essentially the entire complex I from the yeast Y. lipolytica, not just the 14 core subunits.

[Part (a) from Schafer, E., et al., “Architecture of active mammalian respiratory chain supercomplexes,” J. Biol. Chem. 2006 Jun 2; 281(22):15370-5. Epub 2006 Mar 20. Part (b) from Proc. Natl. Acad. Sci. USA 2011. 108(37):15196-15200, Fig. 2A and 3A, “Interaction of complexes I, III, and IV within the bovine respirasome by single particle cryoelectron tomography,” by Dudkina et al.]