(A) The superimposed active-site side chains of wild-type MnSOD and Y34N are colored yellow and green, respectively. Water molecules in wild-type MnSOD and Y34N are colored yellow and red, respectively. The Y34N hydrogen bond relay is illustrated by green spheres. Bond distances are annotated in angstroms. (B) The Y34A active site structure with the hydrogen bonding relay is colored pale cyan. (C) The Y34H active site structure, with the hydrogen bonding relay and distances is annotated in angstroms. (D) Superimposed active site structures of the human wild-type MnSOD and Y34V are colored yellow and blue respectively. The waters colored in red belong to Y34V while the hydrogen bond relay of Y34V MnSOD is illustrated by blue spheres. Bond distances are annotated in angstroms. Adapted with permission from Perry et al. (2009) [5]. Copyright 2009 American Chemical Society.