Figure 8.

X-ray structures of the DCU derivative of bovine heart CcO. (A) The MR/DM electron density maps and the atomic models of the X-ray structure of the native and DCU derivative at Glu90 in stereo-view. The dotted lines denote hydrogen bonds. The red structures represent sections of fatty acid tails. (B) The effect of DCU derivative formation on the conformation of the phospholipids of subunit III. Blue and red structures denote the DCU derivative and native structures, respectively. The red dotted surfaces represent the molecular surfaces of the native structure determined by using a probe radius of 1.1 Å, which determines O₂ accessible surface. (C) Effect of DCU derivative formation on the structure of the potential O₂ pathway. The definition of the blue dotted surface is described in (B). Cross-sections of CcO parallel to the membrane surface at the level of heme a₃ iron and Cu_B denoted by cyan balls are shown in the native and DCU derivative forms. C^α-backbone structures of subunits I (yellow) and III (green) are depicted as thin sticks. A possible O₂ movement in the pathway is shown by a block dotted line. The connection of the two pathways in subunits I and III is clearly seen in the native form. PG1 and PG2 in subunit III are shown in pink and magenta, respectively.