SS-31 vs MOTS-c: Mitochondrial Peptides in Research (2026)

SS-31 and MOTS-c turn up together in nearly every conversation about mitochondrial peptides, so people start to treat them as a matched pair. Put SS-31 vs MOTS-c side by side, though, and the resemblance ends at the address label. One is a four-unit peptide built by chemists to cling to the inner mitochondrial membrane. The other is a 16-unit messenger encoded in mitochondrial DNA, and in cell studies it travels all the way to the nucleus.

Below you’ll find what each one is, where it acts, how far the evidence has come, its US status in 2026 and how to check a batch before it reaches the bench.

Cellugenix supplies SS-31 and MOTS-c strictly for laboratory research. They are not for human or veterinary use. This article is an educational overview of published laboratory research.

Quick answer: What’s the difference between SS-31 and MOTS-c?

SS-31 (elamipretide) is a synthetic four-amino-acid peptide that binds cardiolipin in the inner mitochondrial membrane and is studied for membrane stability. MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA and studied as a metabolic signal that activates AMPK. Both target mitochondria, through different and complementary mechanisms.

✓ Different targets: the membrane (SS-31) and cell signaling (MOTS-c)

✓ Evidence ranges from human trials and an FDA approval (SS-31) to mostly animal data (MOTS-c)

✓ They aren’t interchangeable

Contents

1. SS-31 vs MOTS-c at a glance
2. What is SS-31 (elamipretide)?
3. What is MOTS-c?
4. The difference between SS-31 and MOTS-c
5. Where each one acts
6. What the research shows
7. Where NAD+ fits
8. Are they studied together?
9. US and FDA status
10. How to verify a research batch
11. FAQs

SS-31 vs MOTS-c at a Glance

Quick answer: SS-31 vs MOTS-c comes down to structure against signal. SS-31 is a synthetic tetrapeptide that anchors to cardiolipin on the inner mitochondrial membrane. MOTS-c is a natural mitochondrial-derived peptide that switches on AMPK and can enter the nucleus. SS-31 has one FDA-approved form. MOTS-c has no approval for any use.

	SS-31 (elamipretide)	MOTS-c
What it is	Synthetic tetrapeptide (Szeto-Schiller peptide)	Mitochondrial-derived peptide (MDP)
Natural or synthetic	Synthetic	Encoded in mitochondrial DNA (12S rRNA region)
Size	4 amino acids	16 amino acids
Primary action	Membrane stabilization	Metabolic signaling
Cellular target	Cardiolipin, inner mitochondrial membrane	AMPK pathway; moves to the nucleus under stress
Research focus	Electron transport, oxidative stress, aged and injured tissue models	AMPK signaling, metabolic and aging models (cell culture and mouse)
Human evidence	Multiple clinical trials, up to Phase 3	Very limited; an analog completed an early-stage trial
US regulatory status	FDA accelerated approval for Barth syndrome only (Forzinity, 2025)	Not approved

The table hides one striking contrast. SS-31 was drawn up at a lab bench, one careful tweak at a time. MOTS-c was already in every cell, waiting for someone to read the right stretch of DNA.

Values like purity change from batch to batch, so pair this overview with the SS-31 and MOTS-c batch COAs for the vials you’re working with.

What Is SS-31 (Elamipretide)?

Quick answer: SS-31 is a synthetic tetrapeptide, D-Arg-Dmt-Lys-Phe-NH2, that crosses cell membranes and gathers at the inner mitochondrial membrane. There it binds cardiolipin, the lipid that holds the electron transport chain’s protein complexes in position. Researchers study it for membrane stability and oxidative stress.

The “SS” is a tribute to its designers. Hazel Szeto at Weill Cornell Medicine and Peter Schiller at the Montreal Clinical Research Institute built the Szeto-Schiller peptide series, and in 2004 Szeto saw one member head straight for mitochondria. She founded Stealth Peptides, today Stealth BioTherapeutics, in 2006 to move it toward the clinic. Cardiolipin is found almost entirely in the inner mitochondrial membrane, so a peptide that seeks it out ends up concentrated right where energy is made.

Two decades later, Szeto described the FDA approval to Weill Cornell Medicine as “my dream come true.”

Lab work on SS-31 clusters around four questions:

• Cardiolipin binding: how the peptide holds the folded inner membrane (the cristae) in shape.
• Electron transport: whether energy-producing complexes run more efficiently when cardiolipin is protected.
• Reactive oxygen species: how much oxidative damage builds up in stressed cells with and without the peptide.
• Tissue models: aged and injured heart, kidney, skeletal muscle and retina in animals.

Batch details for the research-grade compound are on the SS-31 10 mg specification and COA page.

Is SS-31 the Same as Elamipretide?

Yes. It’s one molecule with three names. SS-31 is the lab code from the Szeto-Schiller series, elamipretide is its generic drug name, and Forzinity is the approved medicine from Stealth BioTherapeutics. Research-grade SS-31 shares the same sequence, yet it’s a laboratory reagent and a separate product from Forzinity.

Why Is Barth Syndrome Important to SS-31?

Barth syndrome is a rare inherited disease caused by mutations in the TAFAZZIN gene, which leave cardiolipin malformed. About 150 people in the US have it, most of them boys and men. A cardiolipin-binding peptide was a natural candidate, and the FDA granted elamipretide accelerated approval as Forzinity in September 2025 for patients weighing at least 30 kg, according to its FDA prescribing information.

What Is MOTS-c?

Quick answer: MOTS-c is a 16-amino-acid mitochondrial-derived peptide encoded in the 12S rRNA gene (MT-RNR1) of mitochondrial DNA. A USC team led by Changhan David Lee and Pinchas Cohen first described it in Cell Metabolism in 2015. It acts as a metabolic signal that reaches well beyond the mitochondrion.

The 12S rRNA gene was long thought to do one job: build part of the mitochondrial ribosome. Tucked inside it are short open reading frames that produce their own peptides. Humanin was the first one found, followed by six small humanin-like peptides (SHLP1 to SHLP6), and MOTS-c joined the family in 2015.

MOTS-c research falls into four threads:

• AMPK activation: MOTS-c slows the folate cycle, which lets AICAR build up. AICAR switches on AMPK, the enzyme that acts as the cell’s fuel gauge.
• Metabolic models: Lee’s 2015 study examined it in cultured cells and in mice fed a high-fat diet.
• Exercise and aging: Reynolds et al. (2021, Nature Communications) measured MOTS-c in skeletal muscle after exercise and tested it in older mice.
• Nuclear signaling: Kim et al. (2018, Cell Metabolism) showed it moving into the nucleus under metabolic stress, where it binds genes controlled by the antioxidant regulator NRF2.

The exercise work produced the field’s most quoted line. Lee told USC Leonard Davis School of Gerontology the findings suggest you can “rejuvenate an older mouse so it is as fit as a younger one.”

Both research sizes have batch pages: the MOTS-c 40 mg specification and COA and the MOTS-c 10 mg listing.

What Is the Difference Between SS-31 and MOTS-c?

Quick answer: SS-31 is a synthetic peptide that works structurally, holding the inner mitochondrial membrane together. MOTS-c is a natural peptide that works as a messenger between mitochondria and the rest of the cell. They differ in origin, size, target and evidence, so a result from one tells you little about the other.

Four contrasts go deeper than the summary table:

• Origin: SS-31 uses two unusual building blocks, D-arginine and dimethyltyrosine, which help it resist breakdown by enzymes. MOTS-c is built entirely from the 20 standard L-amino acids found in natural proteins.
• Structure: SS-31 alternates positive charges with ring-shaped aromatic groups, a pattern that lets it pass through membranes without a transporter. MOTS-c is four times longer and acts as a signaling peptide that can leave the mitochondrion.
• Target: SS-31 stays anchored in one membrane. MOTS-c travels from mitochondria to cytoplasm to nucleus.
• Evidence: SS-31 has Phase 3 data and an approved drug behind it. MOTS-c research is younger and mostly preclinical.

So is MOTS-c or SS-31 better? Neither one comes out ahead, because each answers a different research question. SS-31 fits studies of membrane integrity, cardiolipin and oxidative stress. MOTS-c fits studies of AMPK signaling, folate-cycle metabolism and the mitochondria-to-nucleus conversation. Think of a structural engineer and a dispatcher: both keep the building running, from different rooms.

Where Does Each One Act in the Mitochondrion?

Quick answer: SS-31 works at the inner mitochondrial membrane, right beside the electron transport chain, where it binds cardiolipin. MOTS-c starts inside the mitochondrion and then leaves. Under metabolic stress it signals through AMPK in the cytoplasm and crosses into the nucleus to influence gene expression.

Location	Mitochondrial peptide	What happens there
Inner mitochondrial membrane	SS-31	Binds cardiolipin beside the electron transport chain complexes
Mitochondria → cytoplasm → nucleus	MOTS-c	Activates AMPK, then enters the nucleus and binds stress-response genes

SS-31 binding cardiolipin at the inner mitochondrial membrane and MOTS-c signalling to the nucleus

Size helps explain the difference in reach. SS-31 is small and charged enough to slip through membranes on its own and pool wherever cardiolipin is dense. MOTS-c relies on the cell’s signaling machinery to carry its message, which is why its effects show up far from the place it’s made.

What Does the Research Show for SS-31 and MOTS-c?

Quick answer: The evidence runs at two speeds. SS-31 has the deepest human record, with several clinical trials and one FDA approval, although results outside Barth syndrome have been mixed. MOTS-c rests mostly on cell and mouse studies, and so far only an engineered analog, CB4211, has reached early human testing.

	Cell and animal studies	Human studies	US regulatory status
SS-31	Many (heart, kidney, muscle and eye models)	Several trials; mixed results outside Barth syndrome	FDA accelerated approval for Barth syndrome only
MOTS-c	Many (mouse metabolism, exercise and aging)	Very limited; analog CB4211 completed a Phase 1a/1b study	Not approved

Six studies anchor most of what’s written about these two peptides:

• Szeto, 2014 (British Journal of Pharmacology): a review naming SS-31 a first-in-class cardiolipin-protective compound.
• Birk et al., 2013 (Journal of the American Society of Nephrology): SS-31 bound cardiolipin in a rat model of kidney ischemia.
• Campbell et al., 2019 (Free Radical Biology and Medicine): SS-31 lowered redox stress and improved exercise tolerance in aged mice.
• Lee et al., 2015 (Cell Metabolism): the first description of MOTS-c, which prevented diet-induced obesity and insulin resistance in mice.
• Kim et al., 2018 (Cell Metabolism): MOTS-c moved into the nucleus when cells faced metabolic stress.
• Reynolds et al., 2021 (Nature Communications): MOTS-c was described as exercise-induced in skeletal muscle, and older mice given MOTS-c showed greater physical capacity.

Clinical trials show where each program is heading. MMPOWER-3, a Phase 3 elamipretide trial in primary mitochondrial myopathy, didn’t reach its walking-test goal across the whole group. A follow-up analysis spotted a stronger response in patients with nuclear DNA replisome variants, and Stealth is now planning a pivotal trial in POLG-related myopathy. Its Phase 3 ReNEW trial in dry age-related macular degeneration is also underway.

MOTS-c’s human story is earlier. CohBar’s analog CB4211 completed a four-week Phase 1a/1b study in 2021, the first step for a MOTS-c-based compound into clinical testing.

Two-track timeline of SS-31 and MOTS-c research milestones from 2004 to 2026

SS-31 vs MOTS-c vs NAD+: Where Does NAD+ Fit?

Quick answer: NAD+ appears next to SS-31 and MOTS-c in almost every mitochondrial discussion, yet it belongs to a different chemical family. It’s a coenzyme that carries electrons in energy metabolism, cycling between NAD+ and NADH, and enzymes called sirtuins and PARPs consume it. That puts it one level below both peptides, in the fuel supply itself.

	What it is	Where it acts	Peptide?
SS-31	Synthetic tetrapeptide	Inner mitochondrial membrane	Yes
MOTS-c	Mitochondrial-derived peptide	Mitochondria, cytoplasm, nucleus	Yes
NAD+	Coenzyme (dinucleotide)	Energy metabolism across the cell	No

The NAD+ research overview goes further into sirtuins and NAD+ decline, and the NAD+ 500 mg specification and COA page lists batch data. NAD+ research often tracks its decline with age in animal tissues, a theme it shares with MOTS-c, whose levels are also compared in young and aged tissue samples.

Is NAD+ a Peptide?

No. NAD+ (nicotinamide adenine dinucleotide) is a dinucleotide: two nucleotides joined through their phosphate groups, one carrying nicotinamide and the other adenine. Peptides are chains of amino acids linked by peptide bonds, and NAD+ contains none. Cells build it from vitamin B3 precursors such as niacin and nicotinamide riboside.

Are SS-31 and MOTS-c Studied Together?

Quick answer: They’re discussed together far more often than they’re tested together. SS-31 targets membrane structure and MOTS-c targets metabolic signaling, so the pairing makes intuitive sense, but published studies of the combination are very limited. A lab comparing them would run each peptide alone, both together and a vehicle control.

A four-arm design is the only clean way to see whether the two effects add up, overlap or cancel out. Useful readouts would cover both sides: cardiolipin content and oxygen consumption for SS-31, and AMPK phosphorylation and folate-cycle metabolites for MOTS-c.

Cell conditions need matching too. MOTS-c responses depend heavily on metabolic state, such as nutrient levels in the culture medium, while SS-31 effects show most clearly under oxidative stress. Keeping those conditions identical across all four arms keeps the comparison fair.

Labs planning that kind of comparison can source all three compounds through the NAD+, MOTS-c and SS-31 research bundle.

Is SS-31 FDA-Approved? US Status of SS-31 and MOTS-c

Quick answer:

• SS-31: elamipretide has FDA accelerated approval as Forzinity (September 19, 2025) for Barth syndrome only, in patients weighing at least 30 kg. Every other use is investigational.
• MOTS-c: no FDA approval for any use.
• Research grade: SS-31 and MOTS-c sold as laboratory reagents are separate from any approved medicine.

MOTS-c still had a busy 2026. On July 23, the FDA’s Pharmacy Compounding Advisory Committee voted in favor of adding it to the 503A bulks list, reviewed for obesity and osteoporosis. That list names substances licensed pharmacies may use to compound patient-specific prescriptions. The vote is advisory, and the FDA hasn’t made a final decision.

Sport has its own rules. The WADA Prohibited List names MOTS-c under S4.4 as an AMPK activator, banned at all times.

For the wider picture, read about research peptides in the USA and what research use only means.

How to Verify Research-Grade SS-31 and MOTS-c

Quick answer: Start with the batch COA. SS-31 and MOTS-c are so different in size that a mass result tells them apart at a glance: about 640 daltons against about 2,175. Read that identity figure alongside HPLC purity, and confirm both belong to the batch in your hands.

	SS-31 (elamipretide)	MOTS-c
Sequence	D-Arg-Dmt-Lys-Phe-NH2	MRWQEMGYIFYPRKLR
Formula	C32H49N9O5	C101H152N28O22S2
Molecular weight	~639.8 g/mol	~2,174.6 g/mol
Cellugenix batch purity (HPLC)	99.97%	99.41% (10 mg) · 99.68% (40 mg)

The two tests answer different questions. HPLC shows how much of the vial is the main compound, and a mass result confirms that compound is the right one. A Purity by HPLC vial of the wrong peptide would pass the first check and fail the second.

A five-point COA check:

1. Batch number: it matches the label on the vial.
2. HPLC purity: the figure appears with the method named.
3. Mass: when a mass result is reported, it lands near the fact-sheet weight.
4. Lab and date: the testing laboratory and test date are both stated.
5. Storage line: lyophilized powder stays sealed, cold, dry and dark.

Our guides on how to read a peptide COA and HPLC vs mass spectrometry walk through each line in more depth.

Frequently Asked Questions

What are mitochondrial-derived peptides?

Mitochondrial-derived peptides (MDPs) are short peptides encoded in mitochondrial DNA, the small circular genome inside each mitochondrion. They come from small open reading frames hidden inside mitochondrial genes, mainly the 12S and 16S rRNA genes. Humanin, the six SHLPs and MOTS-c are the best-studied members, and researchers study them as signals that carry information from mitochondria to other parts of the cell.

Is MOTS-c an endogenous peptide?

Yes. MOTS-c is an endogenous peptide, encoded by a short sequence inside the mitochondrial 12S rRNA gene, and published studies have detected it in mammalian tissue and plasma samples. That research compares its levels across age groups and exercise conditions. Synthetic MOTS-c used in labs copies the natural 16-amino-acid sequence, MRWQEMGYIFYPRKLR.

What does MOTS-c stand for?

MOTS-c stands for “mitochondrial open reading frame of the 12S rRNA type-c.” The name describes where the peptide is coded: a short readable stretch inside the gene for the mitochondrial ribosome’s 12S RNA.

What other mitochondrial peptides are studied?

Humanin, first reported in 2001, is the oldest known mitochondrial-derived peptide and is studied in cell-survival and oxidative-stress models. SHLP1 to SHLP6 come from the 16S rRNA gene. Epitalon is a useful comparison for SS-31: another synthetic tetrapeptide, studied for telomerase and pineal signaling.

Does Cellugenix publish COAs for SS-31 and MOTS-c?

Yes. Every Cellugenix batch is independently tested for purity and identity before release, and the certificates are kept in a COA library organized by product and batch. Each product page also links its own batch COA, so you can match the HPLC purity figure to the vial you receive and file it with your lab records.

How should lyophilized SS-31 and MOTS-c be stored?

Keep sealed lyophilized vials cold, dry and away from light, and follow the storage line on the product page and batch COA. Limit how often vials warm up and cool down again, since repeated temperature swings and moisture speed up degradation. Our peptide storage and handling guide covers this in more detail.

The Bottom Line

SS-31 and MOTS-c both aim at mitochondria, from opposite ends of the job. SS-31 holds the inner membrane steady and has already become an approved medicine for Barth syndrome. MOTS-c carries messages from mitochondria to the nucleus and recently cleared an FDA advisory vote. Treat them as two tools for two different questions. Cellugenix supplies both for laboratory research use only.

Browse Cellugenix’s mitochondrial research compounds

Sources

• Szeto HH. British Journal of Pharmacology, 2014. PMID 24117165.
• Birk AV et al. Journal of the American Society of Nephrology, 2013. PMID 23813215.
• Campbell MD et al. Free Radical Biology and Medicine, 2019. PMC6588449.
• Lee C et al. Cell Metabolism, 2015; 21(3): 443–454.
• Kim KH et al. Cell Metabolism, 2018. PMID 29983246.
• Reynolds JC et al. Nature Communications, 2021; 12: 470.
• Zheng Y et al. Journal of Translational Medicine, 2023. PMC9854231.
• US FDA. FORZINITY (elamipretide) prescribing information, 2025.
• World Anti-Doping Agency. Prohibited List, 2026.