Updated project metadata. Information on the files related to the respective experiments can be found in the metadata file titled “Metadata_for_Nviennensis_Experiments.xlsx”. The data found here encompasses three related mass spectrometry experiments: 1.) BN-PAGE: Biomass of Nitrososphaera viennensis grown in a bioreactor was lysed and membrane fractions were harvested using an ultracentrifuge. Membrane proteins were extracted using n-dodecyl-beta-D-maltoside (DDM) and loaded on a 3-12% gradient blue native PAGE gel. Selected bands were cut out and analyzed via mass spectrometry. 2.) SDS-Tricine-PAGE of AMO Band: A band containing a large amount of the ammonia monooxygenase complex (AMO) was denatured and run on a 15% SDS-Tricine-PAGE gel to identify individual subunits. 3.) AmoC from SDS-Tricine-PAGE: A band containing a high amount of AmoC from the SDS-Tricine-PAGE gel was processed with three separate digestive enzymes (trypsin, chymotrypsin, or GluC) to identify unique peptides among the six AmoC homologs found in the genome of N. viennensis.