Research Use Only. The information presented here is for scientific and educational purposes. These compounds are not intended for human consumption, self-administration, or therapeutic use.
Introduction
Mitochondria have become a central focus of longevity and cellular bioenergetics research, and two peptides appear frequently in that literature: SS-31 and MOTS-c. Although both are examined in the context of mitochondrial function, they act on entirely different targets. SS-31 (also referenced in the literature as elamipretide or MTP-131) is a synthetic aromatic-cationic tetrapeptide investigated for its association with cardiolipin in the inner mitochondrial membrane. MOTS-c is an endogenous mitochondrial-derived peptide encoded within the mitochondrial 12S rRNA region and studied as a metabolic signaling molecule.
This article compares the two compounds from a research framing only, describing what each has been investigated for in preclinical, in-vitro, and animal models. The distinction matters because the two peptides occupy different conceptual categories: one is examined as a membrane-stabilizing structural agent, the other as a regulator of cellular energy signaling through pathways such as AMPK. Both are offered strictly for research use only, not for human consumption.
Two Peptides, Two Mitochondrial Targets
The mitochondrion is often summarized as the cell’s powerhouse, but its internal architecture is what makes it a rich subject for peptide research. The organelle contains an outer membrane, a highly folded inner membrane that houses the electron transport chain, and a central matrix that holds the mitochondrial genome. SS-31 and MOTS-c engage with different compartments of this structure, which is the central reason the two compounds are not interchangeable in the literature.
The inner membrane and cardiolipin
The inner mitochondrial membrane is folded into structures called cristae, and it is enriched with a distinctive phospholipid known as cardiolipin. Cardiolipin helps organize the protein complexes of the electron transport chain and is closely tied to the efficiency of energy production. Research on SS-31 focuses on this membrane compartment, particularly the peptide’s reported association with cardiolipin.
The mitochondrial genome and derived peptides
Deeper within the organelle, the mitochondrial matrix contains a small circular genome. Short open reading frames within this genome and its ribosomal RNA regions can encode small peptides known as mitochondrial-derived peptides (MDPs). MOTS-c is one of the most studied members of this family, and its origin in the 12S rRNA region distinguishes it fundamentally from a synthesized compound like SS-31.
SS-31: A Cardiolipin-Targeting Tetrapeptide
SS-31 belongs to a class of aromatic-cationic peptides sometimes called Szeto-Schiller peptides, named for the researchers Hazel Szeto and Peter Schiller who characterized them. It is a synthetic tetrapeptide, meaning it is built from four amino acids, and it carries a net positive charge that is thought to contribute to its concentration at the inner mitochondrial membrane. The compound can be reviewed on the SS-31 product page.
Structure and target
The reported sequence of SS-31 is D-Arg-Dmt-Lys-Phe-NH2, with an approximate molecular weight of 639.8 g/mol. Its defining research characteristic is an affinity for cardiolipin. By associating with this phospholipid, SS-31 is investigated for whether it can help preserve the structural organization of cristae under conditions of oxidative stress.
What SS-31 is studied for
In preclinical and in-vitro models, SS-31 (also referenced as elamipretide or MTP-131) has been examined in the context of reactive oxygen species, electron transport chain efficiency, and mitochondrial membrane integrity. These investigations are structural and bioenergetic in nature. None of this work establishes a human use, and the peptide is provided strictly for laboratory research applications.
MOTS-c: A Mitochondrial-Derived Signaling Peptide
MOTS-c, short for mitochondrial open reading frame of the 12S rRNA type-c, represents a different research concept entirely. Rather than being synthesized to target a membrane, it is an endogenous peptide that the mitochondrial genome itself encodes. It was first described by Changhan Lee, Pinchas Cohen, and colleagues in 2015. The compound is listed on the MOTS-c product page.
Structure and origin
MOTS-c is a sixteen amino acid peptide with the reported sequence MRWQEMGYIFYPRKLR and an approximate molecular weight of 2174 g/mol. Its larger size compared with SS-31 reflects its role as a signaling molecule rather than a compact membrane-targeting agent.
What MOTS-c is studied for
Research on MOTS-c centers on cellular energy metabolism. It has been associated with activation of the AMPK pathway, a central sensor of cellular energy status. Studies also describe MOTS-c translocating to the nucleus under conditions of metabolic stress, where it is investigated for its influence on metabolic gene expression. In animal models, researchers have examined its relationship to insulin sensitivity and exercise-related metabolism. Because MOTS-c sits within broader longevity research, it is sometimes studied alongside compounds such as NAD+ that also relate to cellular energy pathways.
SS-31 vs MOTS-c: Side-by-Side Comparison
Both compounds appear in our catalog of research peptides, but a direct comparison highlights how little they overlap beyond the shared mitochondrial theme. The values below reflect commonly reported laboratory attributes and are provided for comparison only.
| Attribute | SS-31 | MOTS-c |
|---|---|---|
| Class | Synthetic aromatic-cationic tetrapeptide (Szeto-Schiller) | Endogenous mitochondrial-derived peptide (MDP) |
| Sequence length | 4 amino acids | 16 amino acids |
| Reported sequence | D-Arg-Dmt-Lys-Phe-NH2 | MRWQEMGYIFYPRKLR |
| Approximate molecular weight | 639.8 g/mol | 2174 g/mol |
| Primary studied target | Cardiolipin (inner mitochondrial membrane) | AMPK signaling and metabolic gene regulation |
| Origin | Chemically synthesized | Encoded in mitochondrial 12S rRNA |
| Research focus | Membrane and cristae stabilization, ROS reduction | Energy sensing, metabolic homeostasis |
| Also referenced as | Elamipretide, MTP-131 | No common alias |
Regardless of which peptide a study examines, verifying identity and purity through third-party testing matters. Our guide to reading a peptide COA explains how to interpret those documents, and published batch certificates provide the underlying data for comparison.
Frequently Asked Questions
What is the difference between SS-31 and MOTS-c?
SS-31 and MOTS-c are both studied in mitochondrial research, but they act on different targets. SS-31 is a synthetic tetrapeptide investigated for its association with cardiolipin in the inner mitochondrial membrane, where research examines membrane and cristae stability. MOTS-c is an endogenous peptide encoded within the mitochondrial genome and studied as a metabolic signaling molecule linked to the AMPK pathway. In short, one is examined as a structural membrane agent and the other as a signaling regulator.
Is SS-31 the same as elamipretide?
In the research literature, SS-31 is commonly referenced under several names, including elamipretide and MTP-131. These labels refer to the same aromatic-cationic tetrapeptide studied for its interaction with the inner mitochondrial membrane. Naming can vary between academic and preclinical sources.
What does MOTS-c target in mitochondrial research?
MOTS-c is studied primarily as a regulator of cellular energy metabolism. Research describes its association with the AMPK signaling pathway and its reported ability to translocate to the nucleus under metabolic stress, where it is investigated for influence on the expression of metabolic genes. This positions MOTS-c as a signaling peptide rather than a membrane-targeting agent.
Can SS-31 and MOTS-c be studied together?
Because the two peptides address different aspects of mitochondrial biology, some research programs examine them within the same broader longevity and bioenergetics framework. SS-31 is associated with membrane structure while MOTS-c is associated with metabolic signaling, so investigators sometimes compare or contrast them. Any such work remains preclinical and for research use only.
What is the molecular weight of SS-31 and MOTS-c?
SS-31 is a four amino acid peptide with an approximate molecular weight of 639.8 g/mol. MOTS-c is a sixteen amino acid peptide with an approximate molecular weight of 2174 g/mol. These values reflect commonly reported laboratory attributes and can vary slightly by source and salt form.
Are SS-31 and MOTS-c approved for human use?
No. Both SS-31 and MOTS-c are research compounds offered for laboratory and educational purposes only. They are not intended for human consumption, self-administration, or therapeutic use, and neither is presented here as an approved product.
References and Further Reading
- Szeto HH and colleagues, research on mitochondria-targeted aromatic-cationic peptides. PubMed: Szeto mitochondria targeted peptide
- Elamipretide (SS-31) and inner mitochondrial membrane research. PubMed: elamipretide mitochondria
- Cardiolipin and cristae organization in bioenergetics. PubMed: cardiolipin mitochondrial membrane
- Lee C, Cohen P and colleagues (2015), identification of MOTS-c as a mitochondrial-derived peptide. PubMed: MOTS-c mitochondrial derived peptide
- MOTS-c and AMPK-dependent metabolic regulation. PubMed: MOTS-c AMPK
- Mitochondrial-derived peptides in metabolic and aging research. PubMed: mitochondrial derived peptides aging
- Reactive oxygen species and mitochondrial dysfunction. PubMed: reactive oxygen species mitochondrial dysfunction
