SS-31 vs MOTS-c
Research Comparison

Research Overview

SS-31 vs MOTS-c compares two mitochondria-linked peptides from different classes. SS-31, also called elamipretide, is a synthetic tetrapeptide that concentrates about 1000-fold in the inner mitochondrial membrane (Zhao et al., 2004), where it binds the phospholipid cardiolipin (Birk et al., 2013). MOTS-c is a 16-residue peptide encoded in a short open reading frame of the mitochondrial 12S rRNA gene. Its reported actions are signals, through the folate cycle, AMP-activated protein kinase (AMPK) and nuclear gene expression (Lee et al., 2015; Kim et al., 2018).

Their human records differ too: elamipretide has a placebo-controlled trial program and a US accelerated approval for one indication, while MOTS-c has no published human trial. Disguised Alpha supplies SS-31 (10MG, 50MG) and MOTS-c (10MG, 40MG) as lyophilized powder for laboratory research use only.

Structure and Class

SS-31 is D-Arg-Dmt-Lys-Phe-NH2, where Dmt is 2,6-dimethyltyrosine: C32H49N9O5, about 639.8 g/mol (PubChem CID 11764719). A Szeto-Schiller peptide, it alternates aromatic and basic residues, and two of its four residues, a D-arginine and dimethyltyrosine, are non-standard. In the founding study, analogs without dimethyltyrosine did not inhibit mitochondrial reactive oxygen species generation or swelling (Zhao et al., 2004).

MOTS-c is a natural sequence of 16 standard amino acids with a free carboxyl end, MRWQEMGYIFYPRKLR: C101H152N28O22S2, about 2174.6 g/mol (PubChem CID 146675088). Its discovery followed humanin, another signaling peptide encoded in a short mitochondrial reading frame (Lee et al., 2015).

Both are cationic: SS-31 by design, MOTS-c through three arginines and a lysine. MOTS-c is about 3.4 times heavier, so one milligram holds about 1.56 µmol of SS-31 but about 0.46 µmol of MOTS-c as free peptides. The product pages and PubChem agree on both identities. Supplied material is often a salt, which adds mass; PubChem lists triacetate and trifluoroacetate MOTS-c records for the same peptide.

Side by Side

Research Context: SS-31

The founding study screened peptide antioxidants built on alternating aromatic and basic residues. In neuronal N2A cells they reduced intracellular reactive oxygen species and cell death caused by t-butylhydroperoxide. In isolated mitochondria they lowered reactive oxygen species production, inhibited the permeability transition and swelling, and prevented calcium-induced cytochrome c release (Zhao et al., 2004).

Using a polarity-sensitive fluorescent analog, a later study reported high-affinity binding to cardiolipin, the anionic phospholipid that inner-membrane cristae need. The SS-31 and cardiolipin complex inhibited cytochrome c peroxidase activity by protecting its heme iron, and rats given SS-31 before kidney ischemia kept their cristae without mitochondrial swelling (Birk et al., 2013). In model and mitochondrial membranes, the peptide partitioned into the interfacial region with an affinity tied to surface charge, did not destabilize lamellar bilayers, and altered lipid packing and surface electrostatics (Mitchell et al., 2020).

A rat heart ischemia-reperfusion study measured the respiratory chain directly. In permeabilized ventricular fibers, losses of complex I, II and IV activity were smaller with elamipretide, and 3D electron microscopy showed less fragmentation of cristae networks, though cardiolipin concentration still fell (Allen et al., 2020).

Human research history: the phase 3 placebo-controlled trial in primary mitochondrial myopathy, with 218 participants, met neither primary endpoint (Karaa et al., 2023). A phase 2 placebo-controlled trial in 71 participants with heart failure with reduced ejection fraction found no significant change in left ventricular end systolic volume at four weeks (Butler et al., 2020). In September 2025 elamipretide was granted accelerated approval in the United States, under the brand name Forzinity, for one indication in Barth syndrome, the first disease-specific approval for that condition; a confirmatory trial is required (Shirley, 2026).

That approval covers that drug product for that indication only. The SS-31 sold here is research-grade powder, not that product, and not for use in people.

Research Context: MOTS-c

The discovery paper reported that MOTS-c inhibits the folate cycle and its tethered de novo purine biosynthesis, which leads to accumulation of the intermediate AICAR and activation of AMPK, with skeletal muscle as the apparent primary target organ. In mice it prevented insulin resistance induced by a high-fat diet (Lee et al., 2015). Models: cell culture and mice.

In cultured cells under metabolic stress, MOTS-c moved to the nucleus in an AMPK-dependent way, regulated a broad range of genes in response to glucose restriction, including genes with antioxidant response elements, and interacted with transcription factors such as NFE2L2 (NRF2) (Kim et al., 2018). In two transgenic mouse strains, changes in muscle mitochondrial bioenergetics after MOTS-c depended on both PGC-1 alpha and AMPK, with no apparent change in respiratory protein content and lower mitochondrial reactive oxygen species emission (Gudiksen et al., 2026).

Human research history: the published interventional work is cell culture and rodent research with synthetic peptide, and no human trial has reported findings. ClinicalTrials.gov lists one registered phase 2a placebo-controlled study (NCT07505745) as recruiting. MOTS-c has no approved drug product anywhere, and a review notes that no established clinical application exists (Zheng et al., 2023).

Human papers measure the endogenous peptide, and the method matters. A validated mass spectrometry method built for anti-doping testing reached a detection limit of 100 pg/mL in plasma but could not confirm the 45.9 to 218.5 ng/mL that a commercial ELISA reported in 20 healthy subjects (Knoop et al., 2019).

Choosing Between Them for a Research Question

Membrane and respiratory-chain questions point to SS-31: cardiolipin binding, cristae architecture, complex activity, cytochrome c peroxidase activity, the permeability transition and membrane surface charge, all testable directly in isolated mitochondria and model membranes (Zhao et al., 2004; Mitchell et al., 2020).

Signaling questions point to MOTS-c: folate and purine metabolism, AICAR and AMPK activation, nuclear translocation, antioxidant response element genes and PGC-1 alpha dependent changes in muscle. Because cells make MOTS-c, samples carry an endogenous baseline, so record the assay used (Knoop et al., 2019). SS-31 has no natural background.

Both lowered mitochondrial reactive oxygen species output in published models (Zhao et al., 2004; Gudiksen et al., 2026), so that readout alone cannot separate them. Pair it with a mechanism readout, cardiolipin binding for SS-31 or AMPK activation for MOTS-c, and compare them on moles, not milligrams.

Handling and Storage

Both ship lyophilized, and both product pages list the same storage: -20°C for the powder as shipped, 2 to 8°C after reconstitution, protected from light, with freeze/thaw cycles avoided. Let a sealed vial reach room temperature before opening, and aliquot stock into single-use volumes.

SS-31 is strongly cationic and partitions into anionic lipid interfaces by surface charge (Mitchell et al., 2020), so anionic buffer components or plasticware can shift its free concentration. MOTS-c carries two methionines and a tryptophan that can oxidize, and the anti-doping method tracked two oxidation products (Knoop et al., 2019), so limit air and light and prepare working solutions fresh. For molar work, use the measured content on the lot certificate in the COA portal.

Questions Researchers Ask

SS-31 vs MOTS-c: what is the main difference?

Class and target. SS-31 is a synthetic tetrapeptide that binds cardiolipin in the inner mitochondrial membrane (Birk et al., 2013). MOTS-c is a 16-residue peptide encoded in mitochondrial DNA that acts through the folate cycle, AMPK and nuclear gene expression (Lee et al., 2015; Kim et al., 2018).

Is elamipretide the same as SS-31?

Yes. They are names for the same molecule, which also carried the development codes MTP-131 and Bendavia (PubChem CID 11764719). The approved drug is made and labeled for clinical use; the SS-31 sold here is research-grade powder for laboratory use only.

Elamipretide vs MOTS-c: which has human trial data?

Elamipretide. Its trials in primary mitochondrial myopathy and in heart failure with reduced ejection fraction did not meet their primary endpoints (Karaa et al., 2023; Butler et al., 2020), and it received accelerated approval in the United States in September 2025 for one indication in Barth syndrome (Shirley, 2026). MOTS-c has no published human trial.

MOTS-c vs SS-31: do both work inside mitochondria?

Not in the same way. SS-31 acts at the inner membrane, binding cardiolipin and changing surface electrostatics (Mitchell et al., 2020). MOTS-c is encoded in mitochondrial DNA, but its reported actions are signals, through AMPK and, under metabolic stress, in the nucleus (Kim et al., 2018).