Structural detail of the cytochrome oxidase from R. sphaeroides (2) showing (A) likely hydrogen bonds from N139 to Waters 6614, 6574, 6584 and 6638. (B) Hydrogen bonding of N121 to Water6574 and Water6584, and the hydrogen bonding between these water molecules and Water6638. (C) Hydrogen bonding of N207 to Water6638 and the interactions between waters 6638, 6574, and 6584. The distances from N207 to Water6574, and between Water6638 and Water6584 are too large to predict hydrogen bonds. Distances are indicated in Ångstroms. From (PDB code :2GSM).