Abstract
Nitric oxide reductase (NOR) is a transmembrane enzyme that catalyzes reductive coupling of two molecules of nitric oxide NO to form nitrous oxide N2O in microbial denitrification process. Recently, we solved the crystal structures of two types of bacterial NORs, cNOR and qNOR. As has been proposed, their overall structures are similar to those of aerobic and microaerobic respiratory enzymes, cytochrome c oxidases, supporting the idea that NORs are classified as the divergent members of respiratory Heme-Cupper oxidase superfamily. By comparing these structural data in detail, we can briefly describe functional conversion of the respiratory enzyme in their molecular evolution.
