Fe(III)-[cytochrome c] + H2O + nitric oxide = Fe(II)-[cytochrome c] + 2 H(+) + nitrite Binds 1 Cu(2+) ion. The Cu(2+) ion is held by residues from each of 2 monomers of the trimer. Nitrite is bound to the Cu(2+) ion site. Pseudoazurin is the physiological electron donor for the Cu-NIR in vitro. Binds 1 Cu(+) ion. The Cu(+) ion is bound within a single monomer. Nitrogen metabolism; nitrate reduction (denitrification); dinitrogen from nitrate: step 2/4. Homotrimer. Under anaerobic growth conditions and by nitrite. The type I copper site in NIR plays a crucial role for electron transfer from pseudoazurin to the type II copper site of NIR, which comprises the catalytic center of NIR for the reduction of nitrite. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven. Belongs to the multicopper oxidase family.