Figure 7.

2D Projection maps of purified monomeric complex IV from E. gracilis obtained by single particle averaging. The monomeric complex IV was purified by a two-step chromatographic procedure in the presence of β-dodecyl-n-maltoside and analyzed by EM. Overlap of the monomeric bovine complex together with the cytochrome c (pdb: 5IY5¹³) over the EM images was performed. (A and B) side view projections; (C and D) ~120° rotated views from A projection along a perpendicular axis to the membrane; (E–H) slightly tilted views: the lower region is tilted by ~10–15° to the front from D projection (E, F) and the upper region is tilted by ~10–15° to the front from D projection (G, H). The membrane region is indicated by the green arrow heads, the “helmet-like” domain (see text for details) is indicated with red and yellow arrow heads, Cox5A and Cox5B positions in bovine complex IV (purple arrow heads). At the right: schematic representation of the rotation of the complex in the left panels. The approximate rotation angles over the axis are indicated. The scale bar is 10 nm.