Active site of the metalloenzyme bovine Cu,Zn superoxide dismutase, with ligand side chains including the shared histidine.  Geometry of the ligand atoms is tetrahedral for the Zn and distorted square-planar for the Cu.  From the original 2SOD crystal structure.
Dcrjsr
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>