Each unit of the trimer contains two copper atoms. The coordination environment of one of the copper atoms (Cu I) is comprised of two histidine ligands, a methionine ligand and a cysteine ligand (type I copper protein).

The other copper atom (Cu II, type II copper protein) is coordinated by three histidine ligands (one of which comes from the neighbouring domain). The fourth position is occupied by the substrate (NO₂^-).