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Using a noninvasive, solid-state magic-angle spinning nuclearmagnetic resonance (MAS NMR) approach, we track ex vivo thebehavior of individual membrane components in isolated, activemitochondria (model system: potato tubers) during physiologicalprocesses. The individual phosphatidylcholine (PC), phosphatidylethanolamine(PE), and cardiolipin (CL) membrane constituents were identifiedas distinct lines by applying MAS ³¹P NMR on extracted lipidmembranes. However, the CL NMR signal appeared to be very broadin functional mitochondria, indicating a tight complex formationwith membrane protein. Calcium stress induced severe membranedegradation without recovery of a single CL NMR resonance. Thissuggests that calcium overload destroys the outer mitochondrialmembrane and does not modify strongly the CL protein complexesin the inner membrane; a conclusion confirmed by respiratorycontrols. Conversely, mitochondrial membrane disruption on timedegradation or mechanical stress generates clearly visible identicalCL NMR signals, similar to those observed in rehydrated lipidextracts. Similarly, noninvasive based NMR tracking of lipidsin response to diverse physiological stimuli can easily be usedfor other organelles and whole living cells. Sani, M.-A., Keech,O., Gardeström, P., Dufourc, E. J., Gröbner, G. Magic-anglephosphorus NMR of functional mitochondria: in situ monitoringof lipid response under apoptotic-like stress.