We identified DNAJC30 as a key protein in the maintenance of functional NADH:ubiquinone oxidoreductase (complex I). To determine the turnover rates of modules in complex I and other mitochondrial complexes, we pulsed both patient and control fibroblast cell lines and a DNAJC30 knock-out HEK and control HEK cell line over 12 hours with heavy amino acids (PulseSILAC) followed by mass spectrometry.