Fe(III)-[cytochrome c] + H2O + nitric oxide = Fe(II)-[cytochrome c] + 2 H(+) + nitrite Binds 1 Cu(+) ion. Binds 1 Cu(2+) ion. Nitrogen metabolism; nitrate reduction (denitrification); dinitrogen from nitrate: step 2/4. Homotrimer. 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.