Updated project metadata. Mitochondrial I+III2 supercomplex was purified from Arabidopsis thaliana cells using differential centrifugation including Percoll step gradients and continuous sucrose gradients. Supercomplex fractions were digested with trypsin using the SP3 approach. Peptides were further purified with SepPak cartridges and measured by HPLC-ESI-TIMS-TOF-MS. Database search was performed with MaxQuant (Version 2.0.3.0.) Over 1,300 proteins were identified using this highly sensitive approach, including all known subunits of the I+III2 supercomplex. This MS analysis is part of a publication on the structure of the I+III2 supercomplex from Arabidopsis by Klusch et al., 2022.