NarK monomer with NO2 - source: [http://www.rcsb.org/pdb/explore.do?structureId=4JRE 4JRE]
NirS dimer with N2 - source [http://www.rcsb.org/pdb/explore/explore.do?structureId=1nno 1NNO]
Hao - source [http://www.rcsb.org/pdb/explore.do?structureId=1fgj 1FGJ]