SS-31 (Elamipretide)

SS-31 (Elamipretide, D-Arg-Dmt-Lys-Phe-NH2) is a synthetic tetrapeptide with a unique property among mitochondria-targeted research compounds: it concentrates in the inner mitochondrial membrane through direct electrostatic and hydrophobic interaction with cardiolipin — without requiring the large negative mitochondrial membrane potential (approximately -180 mV) that drives accumulation of most cationic mitochondria-targeted compounds (such as triphenylphosphonium conjugates and MitoQ).

Cardiolipin is a unique phospholipid exclusive to the inner mitochondrial membrane, where it constitutes approximately 20% of total lipids. Its distinctive bis-phosphatidyl glycerol structure — two phosphatidic acid moieties connected through a single glycerol — creates a highly anionic lipid (4 fatty acyl chains, 2 phosphate groups, net charge -2 at physiological pH) that anchors multiple inner membrane proteins: cytochrome c (electron carrier between Complex III and Complex IV), individual electron transport chain complexes (Complex I, III, IV), ATP synthase oligomers, and the adenine nucleotide translocase (ANT). SS-31's alternating cationic (D-Arg, Lys) and aromatic (Dmt = 2',6'-dimethyltyrosine, Phe) residues create an amphipathic peptide that binds cardiolipin's anionic phosphate groups electrostatically and inserts into the cardiolipin acyl chain region hydrophobically.

This cardiolipin binding has two research-relevant consequences. First, SS-31 protects cardiolipin from peroxidation by reactive oxygen species — particularly hydroxyl radicals generated by Fenton chemistry at the inner membrane. Cardiolipin peroxidation disrupts its high-affinity interaction with cytochrome c, causing cytochrome c to dissociate from the inner membrane into the intermembrane space. When the outer membrane is subsequently permeabilised (by BAX/BAK pore formation), free cytochrome c releases into the cytoplasm, activating the apoptosome (Apaf-1/caspase-9 complex) and the intrinsic apoptosis cascade. SS-31 prevents this sequence by blocking the initial cardiolipin peroxidation event.

Second, cardiolipin is essential for ATP synthase dimerisation — the process by which ATP synthase monomers associate in the inner membrane to create the curved cristae ridge architecture that maximises OXPHOS efficiency. Cardiolipin peroxidation impairs ATP synthase dimerisation, flattening cristae and reducing OXPHOS capacity. SS-31 treatment in oxidatively stressed mitochondria has been published to restore ATP synthase oligomeric structure and cristae morphology (Szeto, Pharmacological Sciences, 2014), explaining its effects on respiratory chain function in mitochondrial dysfunction models.

The membrane-potential independence of SS-31 accumulation is its defining pharmacological advantage for research: in ischaemia-reperfusion injury, severe oxidative stress, apoptosis, and heart failure — all conditions where mitochondrial membrane potential is collapsed — potential-dependent compounds (MitoQ, TPP-conjugates) do not accumulate. SS-31 accumulates and functions under all these pathological conditions, making it uniquely useful for studying mitochondrial dysfunction in severe disease contexts.

Research applications: oxygen consumption rate by Seahorse XF (basal, ATP-linked, maximal, spare capacity); TBARS and 4-HNE measurement (lipid peroxidation endpoints); cytochrome c release assay (ELISA of cytosolic fraction); ATP synthase oligomeric structure (blue native PAGE); cristae morphology (TEM); and cardiolipin content measurement (NAO fluorescence, lipidomics).

MW: 639.82 g/mol. CAS: 736992-21-5. Molecular formula: C32H49N7O6. Reconstitute in sterile water at 1mg/mL. Store lyophilised at -20°C. For laboratory and analytical research purposes only.

For mitochondrial membrane potential-independent SS-31 research: this is the key experimental demonstration of SS-31's unique mechanism. Use FCCP (1uM) to fully collapse mitochondrial membrane potential in cells before SS-31 addition. Confirm membrane potential collapse by JC-1 or TMRM fluorescence (shift from red/orange to green indicates depolarisation). Then add SS-31 (100nM-1uM) and measure its cardiolipin protection effects — reduced lipid peroxidation (C11-BODIPY 581/591 fluorescence shift), maintained cytochrome c retention (immunofluorescence), and improved Complex I-IV activity assays in detergent-solubilised mitochondria. Compare with MitoQ (potential-dependent accumulation) which should show no protective effect after FCCP pre-treatment. This experiment directly demonstrates SS-31's potential-independent inner membrane targeting — its defining pharmacological advantage. MW: 639.82 g/mol. CAS: 736992-21-5. Reconstitute in sterile water at 1mg/mL. Store lyophilised at -20°C. For laboratory and analytical research purposes only.