Showing a schematic description of the key elements in the CcO system. The figure considers the pumping elements and the electron (red arrows) and proton (yellow arrows) pathways through the trans-membrane region of the enzyme, i.e. the CuA, the heme a, and the heme a3-CuB binuclear reaction center for the ET; and the conserved E286 residue, the O2 in the binuclear reaction center, intervening water molecules, and the D-propionic and R481 pair where the pumped H+ are believed to leave the mechanistic pumping region.