In all kingdoms of life, the regulation of the function of membrane-bound enzyme via oligomerization is a fundamental aspect of cell physiology. For example, the oligomerization state of an aerobic respiration enzyme, cytochrome c oxidase (CcO), in mitochondrial membrane is known to affect the enzymatic activity. Here, the relationship of the oligomerization state and the function of anaerobic respiration enzyme, membrane-integrated nitric oxide reductase (NOR) was investigated. NOR is evolutionarily related to CcO, and catalyzes reduction of NO to N2O at a heme/non-heme active center. In quinol-dependent nitric oxide reductase (qNOR) from Neisseria meningitidis, the structures of the highly active dimeric and the less active monomeric forms were determined at a resolution of 1.89 and 2.25 Å, respectively, by cryoEM. The comparison of these high resolution structures revealed that broad helical flexibility near the dimer interface of the monomer causes a conformational change in a critical amino acid, Glu563, near the active site, located apart from the dimer interface. In addition, the elimination of the interaction between Glu563 and its surroundings by the mutation of Glu563 increased the population of the monomeric form. These structural information give an idea on the mechanism of the crosstalk between the dimer interface and catalytic site in qNOR. We also explored the oligomerization state of the other NOR, cytochrome c dependent NOR (cNOR) from Pseudomonas aeruginosa, and solved the structure of the dimeric form by cryoEM. The functional study on the dimeric cNOR is underway. Current results provide insights into the role of oligomerization state of NORs in the enzymatic function and its influence on regulating activity.