SS-31, also known as elamipretide, is a small synthetic tetrapeptide that concentrates in the inner mitochondrial membrane and binds the phospholipid cardiolipin. It belongs to the Szeto-Schiller (SS) family of mitochondria-targeted peptides, and it has become a standard research tool for studying how cardiolipin supports electron transport, cristae structure and ATP production. This guide explains the chemistry behind its targeting, summarizes the key studies, and compares it with two other mitochondrial research compounds, MOTS-c and NAD+.
SS-31 is supplied by BioSim for laboratory research only. It is not for human or veterinary use, and nothing here is guidance on administration to people.
Structure: Why SS-31 Reaches the Inner Membrane
SS-31 has the sequence D-Arg-Dmt-Lys-Phe-NH2, where Dmt is 2′,6′-dimethyltyrosine (Birk et al., 2014). The SS peptides share a motif of alternating aromatic and basic residues. Despite carrying a net positive charge, these peptides are cell-permeable and concentrate about 1000-fold in the inner mitochondrial membrane. Dimethyltyrosine adds radical-scavenging capacity: in the original study, analogs without Dmt did not inhibit mitochondrial reactive oxygen species (ROS) generation or swelling (Zhao et al., 2004).
The D-arginine at position 1 and the amidated C-terminus also make the peptide more resistant to peptidases than an all-L sequence would be, which helps in longer cell and animal experiments.
Cardiolipin: The Target
Cardiolipin is a phospholipid with four acyl chains, found almost exclusively in membranes that generate an electrochemical gradient to produce ATP, such as the inner mitochondrial membrane. It interacts with the respiratory chain complexes and substrate carriers, helps organize the electron transport chain into higher-order assemblies called respiratory supercomplexes, and is involved in mitochondrial membrane stability, dynamics and apoptosis (Paradies et al., 2014).
Cardiolipin also controls how cytochrome c behaves. Bound to cardiolipin in one way, cytochrome c carries electrons between complexes III and IV. When the interaction changes, cytochrome c can act as a peroxidase that oxidizes cardiolipin itself, damaging the membrane and the cristae (Szeto, 2014).
Key Findings on SS-31 and Cardiolipin
Several studies built up the current model of how SS-31 works:
- Antioxidant and permeability-transition effects. In neuronal cells and isolated mitochondria, SS peptides reduced intracellular ROS, inhibited the mitochondrial permeability transition and swelling, and prevented calcium-induced cytochrome c release (Zhao et al., 2004).
- Selective cardiolipin binding. Using a fluorescent SS-31 analog, researchers showed high-affinity binding to cardiolipin. The SS-31/cardiolipin complex inhibited cytochrome c peroxidase activity by protecting its heme iron. In a rat model of renal ischemia, pretreatment with SS-31 protected cristae membranes and prevented mitochondrial swelling, and ATP recovered promptly on reperfusion (Birk et al., 2013).
- Membrane interaction and electron transport. SS-31 interacted only with model membranes containing cardiolipin, at about a 1:1 ratio, and NMR showed its aromatic residues penetrating deep into the bilayer. It restored cytochrome c reduction and mitochondrial oxygen consumption in the presence of added cardiolipin, and in fresh mitochondria it increased state 3 respiration and the efficiency of ATP synthesis (Birk et al., 2014).
- Aged muscle energetics. In 27-month-old mice, a single administration of SS-31 restored resting and maximal mitochondrial ATP production, coupling of oxidative phosphorylation and cell energy state in skeletal muscle to young levels within an hour, measured by optical and 31P magnetic resonance spectroscopy. It had no observable effect in young muscle (Siegel et al., 2013).
A review by the peptide’s co-developer summarizes this work and describes SS-31 as the first cardiolipin-protective compound: it prevents cardiolipin from converting cytochrome c into a peroxidase while preserving its electron-carrying function (Szeto, 2014).
SS-31 vs MOTS-c vs NAD+
All three compounds are used in mitochondrial and metabolic research, but they act at very different levels. SS-31 works on membrane structure, MOTS-c on signaling, and NAD+ on cofactor supply.
| Property | SS-31 | MOTS-c | NAD+ |
|---|---|---|---|
| Type | Synthetic tetrapeptide | Mitochondria-derived 16-amino-acid peptide | Dinucleotide cofactor (not a peptide) |
| Primary target | Cardiolipin in the inner mitochondrial membrane | Folate cycle and purine synthesis, leading to AMPK activation | Redox enzymes and NAD+-consuming enzymes (sirtuins, PARPs) |
| Level of action | Membrane structure and electron transport | Cellular and systemic metabolic signaling | Cofactor availability and redox balance |
| Typical readouts | Respiration, cristae morphology, ROS, cytochrome c peroxidase activity | AMPK phosphorylation, insulin sensitivity, glucose uptake | NAD+/NADH ratio, sirtuin activity, metabolic flux |
| Key reference | Birk et al., 2014 | Lee et al., 2015 | Rajman et al., 2018 |
MOTS-c is encoded by a short open reading frame in the mitochondrial 12S rRNA gene. Its primary target organ appears to be skeletal muscle, where it inhibits the folate cycle and de novo purine biosynthesis, leading to AMPK activation (Lee et al., 2015). NAD+ is the cell’s hydrogen carrier for redox reactions and also a signaling molecule that modulates NAD+-sensing enzymes. Its levels decline with age in animal models, which has made NAD+ metabolism a major research theme (Rajman et al., 2018). For a closer look at those two compounds, see our NAD+ vs MOTS-c comparison.
Because the mechanisms differ, the compounds are complementary in study design. A lab investigating age-related decline in mitochondrial function might use SS-31 to test the contribution of cardiolipin and cristae integrity, MOTS-c to probe AMPK-linked metabolic signaling, and NAD+ precursors to test cofactor supply.
Experimental Design Notes
- Measure membrane-level endpoints. Oxygen consumption, membrane potential, ROS production, cristae morphology by electron microscopy and cytochrome c peroxidase activity match SS-31’s proposed mechanism.
- Use stress models. Many effects were seen under stress (ischemia, oxidative challenge, aging) rather than in healthy young tissue (Siegel et al., 2013).
- Include a mechanism control. Analogs lacking dimethyltyrosine lost ROS-related effects in the original work (Zhao et al., 2004), which illustrates the value of structural controls where available.
More context is available in our overview of mitochondrial function and energy metabolism peptides and the longevity research category.
Handling in the Lab
SS-31 is supplied lyophilized. Reconstitute with a suitable sterile diluent, aliquot the stock, avoid repeated freeze-thaw cycles and store as labeled. Our storage and stability guide has more detail.
Frequently Asked Questions
Is SS-31 the same as elamipretide?
Yes. Elamipretide is the nonproprietary name for SS-31 (D-Arg-Dmt-Lys-Phe-NH2).
Does SS-31 work as a general antioxidant?
It has radical-scavenging capacity through dimethyltyrosine (Zhao et al., 2004), but its distinctive feature is selective binding to cardiolipin and modulation of cytochrome c (Birk et al., 2014).
How do I confirm the identity of my lot?
Every BioSim lot is third-party tested, with identity confirmed by mass spectrometry. Available certificates are published on our COA page.
References
- Birk AV, Liu S, Soong Y, et al. (2013). The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. Journal of the American Society of Nephrology : JASN, 24(8), 1250-61. PMID: 23813215 · DOI: 10.1681/ASN.2012121216
- Birk AV, Chao WM, Bracken C, et al. (2014). Targeting mitochondrial cardiolipin and the cytochrome c/cardiolipin complex to promote electron transport and optimize mitochondrial ATP synthesis. British journal of pharmacology, 171(8), 2017-28. PMID: 24134698 · DOI: 10.1111/bph.12468
- Lee C, Zeng J, Drew BG, et al. (2015). The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell metabolism, 21(3), 443-54. PMID: 25738459 · DOI: 10.1016/j.cmet.2015.02.009
- Paradies G, Paradies V, De Benedictis V, et al. (2014). Functional role of cardiolipin in mitochondrial bioenergetics. Biochimica et biophysica acta, 1837(4), 408-17. PMID: 24183692 · DOI: 10.1016/j.bbabio.2013.10.006
- Rajman L, Chwalek K, Sinclair DA (2018). Therapeutic Potential of NAD-Boosting Molecules: The In Vivo Evidence. Cell metabolism, 27(3), 529-547. PMID: 29514064 · DOI: 10.1016/j.cmet.2018.02.011
- Siegel MP, Kruse SE, Percival JM, et al. (2013). Mitochondrial-targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice. Aging cell, 12(5), 763-71. PMID: 23692570 · DOI: 10.1111/acel.12102
- Szeto HH (2014). First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. British journal of pharmacology, 171(8), 2029-50. PMID: 24117165 · DOI: 10.1111/bph.12461
- Zhao K, Zhao GM, Wu D, et al. (2004). Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. The Journal of biological chemistry, 279(33), 34682-90. PMID: 15178689 · DOI: 10.1074/jbc.M402999200
Research These Compounds: SS-31 50mg, MOTS-c 40mg and NAD+ 1000mg from BioSim Peptides: 99%+ purity, every lot third-party tested with identity confirmed by mass spectrometry, and available certificates published on our COA page. For laboratory research use only. Not for human consumption.
