Identification of electron transport supercomplexes in rat heart interfibrillar mitochondria by LC-MALDI-MS/MS analysis. Mitochondrial proteins were separated on a 3-12% Bis-Tris gradient polyacrylamide gel by one-dimensional BN-PAGE. Individual mitochondrial OXPHOS complexes were detected using LC-MALDI-MS/MS analysis. The most representative protein subunits detected for each OXPHOS complex are displayed. I, II, III2, IV and V denote individual OXPHOS complexes. SC to S4 indicate different mitochondrial supercomplexes. All proteins were identified by MASCOT (Matrix Science, Boston, MA, USA) using the parameters described in Materials and Methods. Subunits are named according to the designation approved by the Protein Knowledgebase (UniProtKB) (http://www.uniprot.org/). Results are representative of three mitochondrial preparations.